System and method for carbon dioxide capture and sequestration utilizing an improved substrate structure

ABSTRACT

A structure and system for the adsorption of carbon dioxide from air, the system comprising a sorbent structure comprising a porous substrate having a porous alumina coating on the surfaces of said substrate, and the sorbent for carbon dioxide is embedded on the surfaces of said porous alumina coating. The substrate is preferably a porous monolith, formed from silica or mesocellular foam. The sorbent is an amine group-containing material, preferably loaded at 40 to 60 percent by volume relative to the porous alumina coating.

This application is a continuation of U.S. patent application Ser. No.14/081,534 filed on Nov. 15, 2013, now abandoned, which is acontinuation of U.S. patent application Ser. No. 13/925,679 filed onJun. 24, 2013, now abandoned, which is a continuation of U.S. patentapplication Ser. No. 13/098,370 filed on Apr. 29, 2011, now U.S. Pat.No. 8,500,855, and claims the benefit or priority pursuant to 35 U.S.C.119 (e) from a U.S. Provisional Patent application having ApplicationNo. 61/330,108 filed Apr. 30, 2010; from a U.S. Provisional Patentapplication having Application No. 61/351,216 filed Jun. 3, 2010; from aU.S. Provisional Patent application having Application No. 61/443,061filed Feb. 15, 2011, from U.S. patent application Ser. No. 13/098,370filed on Apr. 29, 2011, now U.S. Pat. No. 8,500,855, and from copendingU.S. patent application Ser. No. 13/925,679 filed on Jun. 24, 2013.

BACKGROUND OF THE INVENTION

The present invention relates to systems and methods for removinggreenhouse gases from an atmosphere, and in particular to systems andmethods for removing carbon dioxide from a stream of gas, including fromthe atmosphere.

As described in copending U.S. application Ser. No. 13/925,679, filed onJun. 24, 2013,

-   -   a. there is much attention currently focused on trying to        achieve three energy related and somewhat conflicting energy        related objectives: 1) provide affordable energy for economic        development; 2) achieve energy security; and 3) avoid the        destructive climate change caused by global warming. However,        there is no feasible way to avoid using fossil fuels during the        rest of this century if we are to have the energy needed for        economic prosperity and avoid energy shortfalls that could lead        to conflict.    -   b. It is mostly undisputed that an increase in the amount of        so-called greenhouse gases like carbon dioxide (methane and        water vapor are the other major greenhouse gases) will increase        the temperature of the planet.    -   c. It is clear that there is no solution that only reduces human        contributions to carbon dioxide emissions that can remove the        risk of climate change. With air extraction and the capability        to increase or decrease the amount of carbon dioxide in the        atmosphere one can in principle compensate for other greenhouse        gases like methane that can change their concentrations and        cause climate change.

SUMMARY OF THE PRESENT INVENTION

The present invention provides further new and useful system and methodconcepts for removing carbon dioxide from a mass of carbon dioxide ladenair by directing the CO₂ laden air through a sorbent structure thatbinds (captures) CO₂, and removing CO₂ from the sorbent structure (andthereby effectively regenerating the sorbent structure) by using processheat, preferably in the form of steam, to heat the sorbent structure. Inthis application, the sorbent structure preferably comprises an aminethat binds to CO₂, and which is carried by a substrate, which can be inthe form of solid particles or be a monolithic sorbent structure.Regardless of whether the substrate is a bed of particulate material ora monolithic form, the sorbent will be preferably adsorbed on thesurfaces of the substrate. In addition, in this application, referenceto a “mass” (or “flow” or “stream”) of “CO₂ laden air (or carbon dioxideladen air)” means air at a particular location with a concentration ofCO₂ that is similar to the concentration of CO₂ in the atmosphere atthat particular location, and at the temperature at that location.

It was previously thought that when carbon dioxide laden air is directedthrough a substrate that is coated with (or has embedded in it) asorbent that absorbs or binds carbon dioxide, to remove the carbondioxide from the air. Process heat converted into the form of steam orother medium (e.g. gas) is directed at the sorbent, to separate thecarbon dioxide from the sorbent (so the carbon dioxide can be drawn offand sequestered), and to regenerate the sorbent (so that the sorbent cancontinue to be used to remove carbon dioxide from the air).

In one of its basic aspects, this application provides additionalstructures and techniques for separating carbon dioxide from carbondioxide laden air, and using process heat to separate carbon dioxidefrom a sorbent and regenerate the sorbent.

Moreover, in another of its aspects, this application provides someadditional structures and techniques that can be used to capture carbondioxide from carbon dioxide laden air, and using process heat toseparate carbon dioxide from a sorbent and regenerate the sorbent, andwhich further enables the carbon dioxide separation and regeneration tobe practiced directly in line with a source of flue gases that wouldotherwise emanate directly from that source and direct carbon dioxideladen air into the atmosphere.

In addition, this invention provides a relatively low cost andrelatively pure CO₂ source for such beneficial uses as feeding algaefarms for biofuel production, where the capture costs represents theentire cost of the CO₂ supply.

These and other features of this invention are described in, or areapparent from, the following detailed description, and the accompanyingdrawings and exhibits.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIGS. 1-9 illustrate the system and method concepts described in anearlier US application by this same inventor, U.S. Ser. No. 12/124,864;Specifically,

a. FIG. 1 is a generalized block diagram of a system for removing carbondioxide from an atmosphere according to an exemplary embodiment of theinvention of U.S. Ser. No. 12/124,864;

b. FIG. 2 is a block diagram of a system for removing carbon dioxidefrom an atmosphere according to an exemplary embodiment of the inventionof Ser. No. 12/124,864;

c. FIG. 3 is a block diagram of an air extraction system according to anexemplary embodiment of the invention of Ser. No. 12/124,864;

d. FIG. 4 is a map illustrating a global thermostat according to anexemplary embodiment of the invention of Ser. No. 12/124,864;

e. FIG. 5 is a block diagram of a system for removing carbon dioxidefrom an atmosphere according to an exemplary embodiment of the inventionof Ser. No. 12/124,864;

f. FIG. 6 is a schematic illustration of one version of a medium forremoving carbon dioxide from an atmosphere and for removing carbondioxide from the medium, according to the invention of Ser. No.12/124,864;

g. FIG. 7 is a schematic illustration of another version of a medium forremoving carbon dioxide from an atmosphere and for removing carbondioxide from the medium, according to the invention of Ser. No.12/124,864;

h. FIG. 8 is a schematic illustration of still another version of amedium for removing carbon dioxide from an atmosphere and for removingcarbon dioxide from the medium, according to the invention of Ser. No.12/124,864; and

i. FIG. 9 is a schematic illustration of yet another version of a mediumfor removing carbon dioxide from an atmosphere and for removing carbondioxide from the medium, according to the invention of Ser. No.12/124,864.

FIGS. 10a and 10b -1, 2 schematically illustrate two versions of astructure and technique for removing carbon dioxide from carbon dioxideladen air, and regenerating the sorbent that absorbs or binds the carbondioxide, according to the principles of the present invention; FIG. 10a, where Absorption Time is significantly greater than Regeneration Time;and FIG. 10b -1, 2, where Absorption Time is approximately equal toRegeneration Time;

FIGS. 10c and 10d are top and side views of one form of elevatorstructure for use in the system and method of FIGS. 10a and 10b -1, 2,in one of its operating positions;

FIGS. 10e and 10f are top and side views of the elevator structure ofFIGS. 10c and 10d , in another of its operating positions;

FIG. 10g schematically shows details of structure that can be used tostrip the captured CO₂ and regenerate the sorbent, in accordance withthe principles of the present invention;

FIG. 10h is a schematic, enlarged illustration of the basic principlesof the elevator structure of the embodiment of FIGS. 10a and 10b -1, 2;

FIGS. 11a and 11b schematically illustrate two other versions of astructure and technique for of removing carbon dioxide from carbondioxide laden air, and regenerating the sorbent that absorbs or bindsthe carbon dioxide, according to the principles of the presentinvention;

FIG. 12 is a schematic illustration of a monolithic, sorbent supportstructure, of a type produced by Corning under the trademark Celcor®,that can be used as a sorbent substrate, in accordance with theprinciples of the present invention.

FIGS. 13A-C are schematic diagrams of a suitable porous substrate,showing the supported amine adsorbent in the pores of each substrate;

FIG. 14 shows a schematic of one example of experimental CO₂ removalapparatus;

FIG. 15 depicts a typical CO₂ desorption profile, in this case for theClass 1 adsorbent, PEI, on a particulate porous silica substrate;

FIG. 16, herein, is a generalized block diagram of a system for removingcarbon dioxide from the atmosphere according to the present invention;

FIGS. 17A-B present generalized flow diagrams showing the successivesteps in a preferred system according to this invention for removingcarbon dioxide from the atmosphere drawing process heat from a carbonburning source, and obtaining a relatively low cost purified stream ofCO₂;

FIGS. 18A-B present generalized flow diagrams showing the successivesteps in a preferred system according to this invention for removingcarbon dioxide from the atmosphere drawing process heat from anon-carbon burning energy source, and obtaining a relatively low costpurified stream of CO₂;

FIG. 19 presents a generalized flow diagram showing the successive stepsin an alternative preferred system according to this invention forremoving carbon dioxide from the atmosphere and obtaining a relativelylow cost purified stream of CO₂;

FIG. 20 presents a more specific flow diagrams showing the successivesteps in the preferred system according to this invention for removingcarbon dioxide from the atmosphere and obtaining a relatively low costpurified stream of CO₂;

FIGS. 21A,B are diagrams showing the preferred chevron shaped formationof the multiple monolith modules of the present invention for thecapturing of one Million Tons of CO₂ from the atmosphere;

FIG. 22 is a schematic illustration of a preferred version of aformation of multiple fans for providing the flow of air through thechevron-shaped formation of CO₂ capture modules when there is no wind;

FIG. 23 is a schematic illustration of a preferred elevator system formoving primary and the CO₂ stripping station; and

FIGS. 24A-C are schematic illustrations showing the elevator structuremoving the sorbent structure between the two stations.

FIGS. 25, 26A and 26B are schematic illustrations showing alternativemeans to inject a small proportion of hot effluent gases into theincoming air to the CO₂ capturing stage.

FIG. 27 represents the change in energy usage and temperature of theadsorbent with varying initial CO₂ content in the incoming gas.

FIG. 28 represents a flow diagram of the two-stage CO₂-removal processembodiment of this invention.

DETAILED DESCRIPTION Background Description of the System and MethodConcepts of Application Ser. No. 12/124,864

Initially, it is believed useful to describe the method and system ofU.S. application Ser. No. 12/124,864, to provide background for theadditional ways the present invention further develops those principles.FIGS. 1-9 illustrate the system and method of U.S. application Ser. No.12/124,864. FIG. 1 is a generalized block diagram of a system, generallydesignated by reference number 1, for removing carbon dioxide from anatmosphere according to an exemplary embodiment of the presentinvention. The system 1 includes an air extraction system 40 and acollection system 50 that isolates the removed carbon dioxide to alocation for at least one of sequestration, storage and generation of arenewable carbon fuel or the generation of a non-fuel product such asfertilizer and construction materials (or to be used in green houses orto enhance the rate of microbial production of biofuels). The airextraction system 40 preferably incorporates any known orlater-discovered CO₂ extraction method, including methods which use amedium (also referred to as a sorbent) to absorb and/or bind (adsorb)CO₂ from the atmospheric air, entering at 2001, by exposing the mediumto chemical, electrical and/or physical interaction with the CO₂ in thecaptured air. The medium may be liquid, gaseous or solid, or acombination of liquid, gaseous and solid substances, where in the caseof solids, the substance is preferably porous. The medium is preferablyrecyclable so that after the CO₂ is captured by the medium and separatedfrom the medium for sequestration, the medium can be reused forabsorption/binding of additional CO₂. As shown in FIG. 1, the separationof the CO₂ from the medium, and the sequestration of the CO₂, enteringvia 2002, performed by the sequestration system 50, may be made moreefficient by the addition of heat, via line 2000, to the air extractionsystem 40. In the present invention, the heat is process heat generatede.g. by a solar energy generator, such as a solar collector, to bedescribed in further detail below. In other embodiments, process heatmay be provided by other types of energy sources, such as, for example,fossil fuel, geothermal, nuclear, biomass, and other renewable energysources. The term “process heat” as used herein refers to the lowertemperature heat remaining after the higher temperature heat has beenused to generate electricity. More generally, the term “process heat”refers to any low temperature heat remaining after a primary process orthat is added by the process itself, such as, for example, exothermiccarbonation reactions in which carbon dioxide is stored as a mineral orin fact when it binds to the medium and is captured. Moreover, “processheat” may be provided from the use of sources of energy to produceproducts other than power or electrical generation. For example, primaryprocessing such as chemical processing, production of cement, steel oraluminum, production of energy products like coal to liquid energyproducts, refining, may use heat to drive the primary processing, andthe unused heat remaining after the primary processing or created duringthe primary processing would be the process heat of such processing, andcan be used in the system or method of the present invention. Aparticularly preferred way of providing process heat is by aco-generation process, in which a primary process (e.g. for generatingelectricity) provides a source of process heat (either directly in theform of steam, or in a form that can be used to heat a body of liquid toproduce steam) and that process heat is further used in the mannerdescribed herein to remove CO₂ from a substrate and regenerate thesorbent carried by the substrate.

Applicants' preferred concept of extracting carbon dioxide from theatmosphere and using process heat to separate carbon dioxide from thecollection medium is a significant way of addressing the global warmingproblem, and goes against the conventional wisdom in the art (and iscounterintuitive to those in the art). Specifically, the use of processheat to solve the global warming problem by extracting carbon dioxide(CO₂) from the low concentration ambient air is very attractive comparedto both the conventional approach of extracting CO₂ from highconcentration flue gas sources and other schemes known in the art forextracting CO₂ from the ambient atmosphere. In the former case it goesdirectly against conventional wisdom that 300 times lower concentrationof the CO₂ in ambient atmosphere would expect it to be 300 times moreexpensive since separation costs are thought to generally scaleinversely with the concentration. Thus most efforts have been directedat extracting CO₂ from the flue gas emissions of power plants (e.g.clean coal) and experts have publicly claimed that the use of ambientair as opposed to flue gas makes no sense. However, the large infinitesize of the ambient air source compared to the finite flue gas sourceand sources generally is one feature that enables applicants' approachto be effective in spite of conventional wisdom and practice. In theflue gas case the emissions containing the CO₂ are at a highertemperature (65-70 degrees centigrade) and therefore sorption mediumregeneration uses higher temperature heat which is more costly than isneeded for the cool ambient air (approximately 25-30° C.). There areother benefits of applicants' approach including the ability to use verythin separation devices that also provide further process improvements.Thus, it could be less costly to remove CO₂ by piping the process heatto a global thermostat facility that operates on the principles ofapplicants' invention, rather than cleaning up directly its flueemissions. In addition, the applicants' approach would produce negativecarbon, actually reducing the amount of CO₂ in the atmosphere, whilecleaning up the flue gas would only prevent the CO₂ content in the airfrom increasing.

Further analysis shows that one cannot solve the global warming problemin a timely manner to reduce the great risk it poses by simply cleaningup large stationary fossil fuel sources like coal plants or for thatmatter by conservation or use of renewables. One needs to actually beable, as is the case in this invention, to extract CO₂ from theatmosphere thus reducing the ambient concentration (“negative carbon”)and reducing the threat of global warming. Other published schemes forextracting CO₂ from the ambient atmosphere have used higher temperatureheat generally and not process heat specifically and therefore have notbeen seriously considered because of their high energy costs.

FIG. 2 is a block diagram of a system, generally designated by referencenumber 2, for removing carbon dioxide from an atmosphere according to anexemplary embodiment of the present invention. The system 2 includes asolar collector 10, an optional supplemental energy source 20, a powergenerator 30, an air extraction system 42 and a collection system 50.Each of these components of the system 1 is explained in detail below.

The solar collector 10 is not a feature of this invention and iswell-known to the art. For example, concentrating solar power parabolicmirrors, and concentrating solar power towers. As is known in the art,the solar collector 10 converts solar energy to thermal energy, whichmay be used to heat a working fluid to drive the power generator 30, vialine 20031. Residual thermal energy (i.e., process heat) may be used todrive the air extraction system 42, via line 20032, and/or thecollection system 50, via line 20033. For example, any process heat leftover after the primary use of the solar heat cat be used to improve theefficiency of chemical and/or physical reactions used in the airextraction system 42 to absorb CO₂ from the air and/or to drive off theCO₂ from the medium.

The power generator 30 may be, for example, a thermal power electricgenerator that converts the thermal energy provided by the solarcollector to electricity. Addition, the thermal energy provided by thesolar collector 10 can be supplemented by energy generated by thesupplemental energy source 20.

Moreover, as described above, “process heat” may be provided from theuse of sources of energy to produce products other than power orelectrical generation. For example, in a co-generation system, primaryprocessing such as chemical processing, production of cement, steel oraluminum, refining, production of energy products like coal and liquidenergy products, may use heat to drive the primary processing, and theunused heat remaining after the primary processing or created during theprimary processing would be the process heat of such processing, and canbe used in a system or method according to the principles of the presentinvention.

FIG. 3 is a block diagram of the air extractor system 42 usable with thesystem 2 according to an exemplary embodiment of the present invention.The air extractor system 42 includes an air contactor 41, a causticizer43, a slaker 45, a calciner 47 and a capture unit 49. The air contactor41 may use a sorbent material to selectively capture CO₂ from the air,and may be composed of a sorbent material which readily absorbs/bindsCO₂ from the air may be an amine that can operate (e.g. capture CO₂, andbe processed to collect the CO₂ and regenerate the sorbent) atrelatively low temperature (e.g. below about 120° C.) or sodiumhydroxide (NaOH) which would operate at significantly highertemperature. As known in the art, amine-enriched solid sorbents may beused to absorb/bind CO₂. Preferably, the sorbent material is regeneratedand the capture method requires less than about 100-120° C. heat toregenerate the sorbent material. Thus, the preferred sorbent material isan amine.

The capture unit 49 may also compress the captured CO₂ to liquid form sothat the CO₂ can be more easily sequestered.

The collection system 50, receiving CO₂ through line 2014, isolates theremoved carbon dioxide to a location for at least one of sequestration,storage and generation of a renewable carbon fuel or the generation of anon-fuel product such as fertilizer and construction materials. Thecollection system 50 may use any known or future-discovered carbon,sequestration and/or storing techniques, such as, for example, injectioninto geologic formations or mineral sequestration. In the case ofinjection, the captured CO₂ may be sequestered in geologic formationssuch as, for example, oil and gas reservoirs, unmineable coat seams anddeep saline reservoirs. In this regard, in many cases, injection of CO₂into a geologic formation may enhance the recovery of hydrocarbons,providing the value-added byproducts that can offset the cost of CO₂capture and collection. For example, injection of CO₂ into an oil ornatural gas reservoir pushes out the product in a process known asenhanced oil recovery. The captured CO₂ may be sequestered underground,and according to at least one embodiment of the invention at a remotesite upwind from the other components of the system 2 so that anyleakage from the site is re-captured by the system 2.

Among the various classes of solid CO₂ adsorbents, supported amines havemany promising features, such as operation at low temperatures(ambient—120° C.). In addition, they have strong CO₂ sorbentinteractions (50-105 kJ/mol), acting as unique, low temperaturechemisorbants [4]. In contrast, most other low temperature adsorbentssuch as zeolites, carbons and (some) MOFs rely on weaker, physisorptioninteractions, making water, a common component in flue gas, out-competeCO₂ for adsorption sites in many cases. Indeed, there are over 70publications in the open literature that explore the CO₂-adsorptionproperties of supported amine adsorbents.

Supported amine CO₂ sorbents are most effectively regenerated in atemperature swing process, as significant energy is necessary to breakthe amine-CO₂ bonds. As noted above, this has most often been achievedin literature reports by providing two driving forces for desorption,(i) a partial pressure driving force by passing a CO₂-free, inert gasflow over the sample, and (ii) a heat input, usually in the form of athermally heated reactor. Two more practical approaches to achievesorbent regeneration are (i) heating the sorbent in a pure, heated CO₂stream and (ii) steam stripping. In the former case, the only drivingforce for desorption is thermal, and the significant gas phase CO₂pressure severely limits how much CO₂ will desorb. It has been shownthat such an approach can also lead to significant deactivation of theamines via urea formation, Drage, T. C., et al., Thermal stability ofpolyethyleneimine based carbon dioxide adsorbents and its influence onselection of regeneration strategies. Microporous Mesoporous Mat., 2008.116: p. 504-512. Nonetheless, this approach could be useful because itgenerates a pure CO₂ stream for sequestration or other uses.

It is now seen that the second approach, steam stripping, is potentiallymuch more promising in the context of low temperature CO₂ capture fromthe atmosphere. Steam stripping provides both (i) a thermal drivingforce for desorption and (ii) a partial pressure driving force, as inthe case of inert gas temperature swing. More importantly, the productstream, containing only CO₂ and water, can be easily purified bycompression, removing the water as a liquid to produce a highlyconcentrated CO₂ gas stream, suitable for sequestration or other use.Furthermore, low grade, low cost steam (saturated, 105° C.—effectivelylow value, waste heat from most processes) can be sufficient to removeCO₂ from the solid sorbent. It can now be demonstrated for the firsttime that steam-stripping is a generally useful approach forregenerating various CO₂-saturated supported amine adsorbents in apractical way.

There are three classes of useful supported amine sorbents. Class 1adsorbents are based on porous supports impregnated with monomeric orpolymeric amines (Figure X). The amine species are thus physicallyloaded onto or into the support. This class of sorbents was pioneered bySong and is described in the technical literature, for example in Xu, X.C., et al., Preparation and characterization of novel CO ₂ “molecularbasket” adsorbents based on polymer-modified mesoporous molecular sieveMCM-41. Microporous Mesoporous Mat., 2003. 62(1-2): p. 29-45 and Xu, X.C., et al., Influence of moisture on CO ₂ separation from gas mixture bya nanoporous adsorbent based on polyethylenimine-modified molecularsieve MCM-41. Ind. Eng. Chem. Res., 2005. 44(21): p. 8113-8119 and Xu,X. C., et al., Novel polyethylenimine-modified mesoporous molecularsieve of MCM-41 type as high-capacity adsorbent for CO ₂ capture. EnergyFuels, 2002. 16(6): p. 1463-1469. Class 2 adsorbents are based on aminesthat are covalently linked to the solid support. This has most oftenbeen achieved by binding amines to oxides via the use of silanechemistry or via preparation of polymeric supports with amine-containingside chains. Class 3 adsorbents are based on porous supports upon whichaminopolymers are polymerized in-situ, starting from an amine-containingmonomer. This Class 3 type was described for use as adsorbents for CO₂capture by Hicks, J. C., et al., Designing adsorbents to CO ₂ capturefrom flue gas-hyperbranched aminosilicas capable, capturing CO ₂reversibly. J. Am. Chem. Soc., 2008. 130(10): p. 2902-2903, and byDrese, J. H., et al., Synthesis-Structure-Property Relationships forHyperbranched Aminosilica CO ₂ Adsorbents. Adv. Funct. Mater., 2009.19(23): p. 3821-3832. Representative examples of each of these adsorbentclasses were prepared for CO₂ capture and steam-regeneration studies.

The Class 1 adsorbent contained low molecular weight Polyethylene Imine(“PEI”), on a commercial, porous particulate silica support, from PQCorporation. The PEI loading was 35% by weight, as measured bythermogravimetric analysis (TGA). The Class 2 adsorbent was obtained bygrafting 3-aminopropyltrimethoxysilane, in a Toluene carrier, to anotherfraction of the same silica support (PQ-Mono). The organic loading, asdetermined by TGA, was 13% by weight. The Class 3 adsorbent was obtainedvia the hyperbranching, in-situ polymerization of aziridine on amesocellular silica foam support, in a Toluene carrier, yielding anorganic loading of 19%. See FIG. 13 for schematic diagrams of the poroussubstrate with the supported amine adsorbent, in the pores of eachsubstrate, respectively, FIG. 13A, FIG. 13B and FIG. 13C. Useful poroussilica supports are also commercially available in monolithic, but thin,structures form, from Corning, for example.

The three supported amine adsorbents were subjected to cyclic adsorptionand desorption tests using CO₂ diluted in nitrogen as the test gas,followed by regeneration of the sorbents by contacting the supportedadsorbents with a 103° C. saturated steam flow of 1.2 g/min for 25minutes in the jacketed reactor vessel. The CO₂-steam mixture producedwas subsequently carried to a Horiba IR-based CO₂ detector by a nitrogenpurge. FIG. 14 shows a schematic of this experimental apparatus. FIG. 15depicts a typical CO₂ desorption profile, in this case for the Class 1adsorbent, PEI on a particulate PQ Corporation porous silica substrate.The adsorbents were exposed to a water-saturated, CO₂-containing feedstream until adsorbent saturation occurred. Subsequently, the jacketaround the reactor was filled with propylene glycol-water solution at105° C. to limit steam condensation on the walls and then saturatedsteam (at about 103° C.) was introduced into the reactor from theautoclave so as to pass through the supported adsorbent to strip theCO₂. The steam effluent showed a very sharp increase in the CO₂concentration, with the CO₂ concentration in the effluent dropping backto essentially zero within 10 minutes. As can be seen by the desorptiontrace in FIG. 15, the vast majority (66%) of the CO₂ was removed in thefirst 3 minutes at a sample temperature of 104° C. These data clearlyshow that low temperature steam-stripping is effective for regeneratingthese supported amine adsorbents.

The data in Table 1, below, show that all three classes of adsorbentsshow some level of stability in the cyclic adsorption/regeneration testsusing steam-stripping. Interestingly, the Class 1 adsorbent appeared tobe quite stable under the steam-stripping conditions used here. In otherwork, higher temperature inert gas temperature swing desorption,stability was less than what would be desired during multipleregeneration cycles with Class 1 adsorbents. It might be anticipatedthat these materials could be the least stable of the three classes ofadsorbents under steam-stripping conditions, due to the lack of covalentbonds between the aminopolymer and the support and the measurablesolubility of low molecular weight PEI in water. Assuming some steamwould condense on the sorbent while transferring heat to the sample, onemight infer that some PEI can be washed out of the sample, as wasobserved in some earlier cases. However, these data suggest that for atleast the three cycles shown here, Class 1 samples can be quite stable.

TABLE 1 CO₂ capacity stability of various supported amine CO₂ adsorbentsin multi-cycles using steam-stripping for sorbent regeneration. CapacityCapacity Capacity Sample Cycle 1^([a]) Cycle 2^([a]) Cycle 3^([a]) Class1 100% 103% 98% Class 2 100% 94% 83% Class 3 100% 115% 103%^([a])Capacities are normalized to the initial capacity found in thefirst experiment.

The Class 3 adsorbent also appears to be stable over three runs with theconditions used. The adsorption capacities in runs 2 and 3 that arelarger than the initial run are suggestive of some polymer restructuringduring the cycles. The Class 2 adsorbent appeared to lose some of itscapacity over the three cycles. At first glance, this is surprising, asone might surmise that these samples should be the most robust, owing tothe covalent Si—C bond connecting the amines to the oxide framework.Nonetheless, even this sample showed significant recyclability, and theslight decrease observed here should not be construed as indicative ofthe overall stability of this class of materials. In total, these dataillustrate a simple but important point: for all the classes ofsupported amine CO₂ adsorbents, there is potential for development ofmaterials that will be stable during regeneration via steam stripping.

The following procedures can be followed to provide amine sorbentsupported on commercial particulate silica supplied by the PQCorporation (PQ-9023) or on mesocellular foam. For the preparation ofall the adsorbents, the silica substrate was first dried under vacuum at100° C. For 24 hrs. to remove absorbed water on the surface before use.A commercial particulate silica supplied by the PQ Corporation (PQ-9023)and a lab-synthesized mesocellular foam were used as supports. Thecommercial silica is characterized by a surface area of 303 m²/g, anaverage pore volume of 1.64 cc/g. and an average pore diameter of 60 nm.The mesocellular foam was prepared following a literature methodology,Wystrach, V. P., D. W. Kaiser, and F. C. Schaefer, PREPARATION OFETHYLENIMINE AND TRIETHYLENEMELAMINE. J. Am. Chem. Soc., 1955. 77(22):p. 5915-5918. Specifically, in a typical synthesis, 16 g of PluronicP123 EO-PO-EO triblock copolymer (Sigma-Aldrich) was used as templateagent and dissolved in 260 g DI-water with 47.1 g concentrated HCl. Then16 g of trimethylbenzene (TMB, 97%, Aldrich) was added at 40° C. andstirred for 2 hrs before 34.6 g tetraethyl orthosilicate (98%, Aldrich)was added to the solution. The solution was kept at 40° C. for 20 hrsbefore 184 mg NH₄F (in 20 mL water) was added. The mixture is later agedat 100° C. For another 24 hrs. The resulting silica was filtered, washedwith water, dried in oven, and calcined at 550° C. in air for 6 hr toremove the organic template before further use. The mesocellular foamsilica is characterized by a surface area of 615 m²/g, an average porevolume of 2.64 cc/g and average window and cell diameters of 12 nm and50 nm.

For the preparation of the Class 1 adsorbent, 1.8 g low molecule-weightpoly(ethylenimine) (PEI, MN˜600, Mw˜800, Aldrich) and 90 mL methanol(99.8%, Aldrich) were mixed first in a 150 mL flask for 1 hr.Subsequently, 3 g of amorphous particulate silica (PQ Corporation,PD-09023) was added and stirred for an additional 12 hrs. The methanolsolvent was later removed by rotavap, and the resulting supportedadsorbent (“PQ-PEI”) was further dried under vacuum at 75° C. overnightbefore testing.

For preparation of the Class 2 adsorbent, 90 mL, anhydrous toluene(99.5%, Aldrich) and 3 g of particulate silica (PQ Corporation) wasmixed in a 150 mL pressure vessel for 1 hr, then 3 g of3-aminopropyltrimethoxysilane (APTMS, Aldrich) was added into themixture. The mixture was kept under vigorous stirring for 24 hr at roomtemperature. The resulting supported adsorbent (PQ-Mono) was recoveredby filtration, washed with toluene and acetone, and then driedovernight, under vacuum, at 75° C.

For the Class 3 adsorbent, particulate mesocellular silica foam (MCF)was reacted with aziridine (a highly reactive but toxic material) in asimilar manner as reported in the literature (Hicks, J. C., et al.,Designing adsorbents for CO ₂ capture from flue gas-hyperbranchedaminosilicas capable, of capturing CO ₂ reversibly. J. Am. Chem. Soc.,2008. 130(10): p. 2902-2903). For this synthesis, 3 g of MCF wasdispersed in 90 mL toluene in a 150 mL pressure vessel and the mixturewas stirred for 1 hr before adding 6 g aziridine (which was synthesizedin accordance with the following procedure, Wystrach, V. P., D. W.Kaiser, and F. C. Schaefer, PREPARATION OF ETHYLENIMINE ANDTRIETHYLENEMELAMINE. J. Am. Chem. Soc., 1955. 77(22): p. 5915-5918),immediately before use. After continuous stirring for 24 hr, theresulting supported adsorbent (MCF-HAS) was filtered, washed withtoluene and ethanol, and dried overnight under vacuum at 75° C.

Steam-stripping and adsorption of CO₂ from the atmosphere was carriedout over several cycles to test the durability of the different forms ofsorbent used. In each case, in the apparatus of FIG. 14, theCO₂-containing gas stream (a mixture of N₂ and CO₂) was passed over 2 gof the supported sorbent at substantially ambient temperature, i.e.,about 20° C., until adsorbent saturation is reached; and the adsorbentwas subjected to steam stripping. Testing apparatus (FIG. 14) wasdesigned and built to allow for the evaluation of steam-strippingsorbent regeneration over multiple cycles. Regeneration of the supportedsorbents is carried out by contacting the supported saturated adsorbentswith 103° C. saturated steam, flowing at 1.2 g/min for 25 minutes. TheCO₂-steam mixture effluent is then carried to a Horiba IR-based CO₂detector by a nitrogen purge [99], for quantification. It should benoted that this nitrogen purge facilitates quantification of the CO₂ andis not necessary in a practical device, thus a true concentration of CO₂can be achieved by condensation of the water in the gas stream,achieving a concentrated CO₂ stream as a product.

In regards to mineral seguestration, CO₂ may be sequestered by acarbonation reaction with calcium and magnesium silicates, which occurnaturally as mineral deposits. For example, as shown in reactions (1)and (2) below, CO₂ may be reacted with forsterite and serpentine, whichproduces solid calcium and magnesium carbonates in an exothermicreaction.1/2Mg₂SiO₄+CO₂=MgCO₃+1/2SiO₂+95 kJ/mole  (1)1/3Mg₃Si₂O₅(OH)₄+CO₂=MgCO₃+2/3SiO₂+2/3H₂O+64 kJ/mole  (2)

Both of these reactions are favored at low temperatures, which favor anamine as the sorbent. In this regard, both the air capture and airsequestration processes described herein may use electricity and/orthermal energy generated by the solar collector 10 (or other renewableenergy source) to drive the necessary reactions and power theappropriate system components. In an exemplary embodiment of the presentinvention, a high temperature carrier may be heated up to a temperaturein a range of about 400° C. to about 500° C. to generate steam to run agenerator for electricity, and the tower temperature and pressure steamthat exits from the electrical generating turbines can be used to driveoff the CO₂ and regenerate the sorbent (e.g., an amine at lowtemperatures or NaOH at higher temperatures). The temperature of thehigh temperature heat, the generated electricity and the temperature ofthe lower temperature process heat remaining after electricityproduction can be adjusted to produce the mix of electricity productionand CO₂ removal that is considered optimal for a given co-generationapplication. In addition, in exemplary embodiments, still lowertemperature process heat that emerges out of the capture andsequestration steps may be used to cool equipment used in these steps.

One or more systems for removing carbon dioxide from an atmosphere maybe used as part of a global thermostat according to an exemplaryembodiment of the present invention. By regulating the amount of carbondioxide in the atmosphere and hence the greenhouse effect caused bycarbon dioxide and other gas emissions, the system described herein maybe used to alter the global average temperature. According to at leastone exemplary embodiment of the present invention, several carbondioxide capture and sequestration systems may be located at differentlocations across the globe so that operation of the multiple systems mabe used to alter the CO₂ concentration in the atmosphere and thus changethe greenhouse gas heating of the planet. Locations may be chosen so asto have the most effect on areas such as large industrial centers andhighly populated cities, or natural point sources of CO₂ each of whichcould create locally higher concentrations of CO₂ that would enable morecost efficient capture. For example, as shown in FIG. 4, multiplesystems 1 may be scattered across the globe, and internationalcooperation, including, for example, international funding andagreements, may be used to regulate the construction and control of thesystems 1. In this regard, greenhouse gases concentration can be changedto alter the average global temperature of the planet to avoid coolingand warming periods, which can be destructive to human and ecologicalsystems. During the past history of our planet, for example, there havebeen many periods of glaciation and rapid temperature swings that havecaused destruction and even mass extinctions. Such temperature swings inthe future could be a direct cause of massive damage and destabilizationof human society from conflicts resulting from potential diminishedresources. The global thermostat described herein may be the key topreventing such disasters in the decades to come.

FIG. 5 is a block diagram of a system, generally designated by referencenumber 100, for removing carbon dioxide from an atmosphere according toanother exemplary embodiment of the present invention. The system 100includes a renewable energy source 110 (which provides Heat to the PowerGenerator, the Air Extraction System and the Collection System via lines20161, 20163 and 20164, respectively, an optional supplemental energysource 120, which provides heat via line 20162 to a power generator 130,an air extraction system 142, sending carbon dioxide through line 2019to a collection system 150. The present embodiment differs from theembodiment of FIG. 2 in that the renewable energy source 110 may be anyknown or future-discovered energy source besides solar, such as, forexample, nuclear, geothermal, and biomass energy sources. Preferably,the renewal energy source produces thermal energy, which can be used toproduce electricity and to improve the efficiency of the variouschemical and/or physical reactions that take place within the airextraction system 142 and the collection system 150. In this regard, theair extraction system 142 and the collection system 150, via tines20161, 20162, 20163 and 20164, respectively, and sending process heatvia line 2017. May be the same as described with reference to theprevious embodiment, or may include components according to any otherknown or future-discovered air extraction and collection systems. Inaddition, as shown in the global map of FIG. 4 with reference to theprevious embodiment, a plurality of systems 100 can be strategicallyplaced across the globe, and control of the systems 100 can becoordinated so as to collectively function as a global thermostat.

FIGS. 6-9 are schematic illustrations of several ways that carbondioxide can be removed from an atmosphere, according to the principlesof the present invention.

Specifically, in FIG. 6, a pair of substrates 600, 602 are illustrated,each of which has a medium (e.g. NAOH, an amine or other suitablesorbent) that can be brought into contact with an atmosphere to removecarbon dioxide from the atmosphere. The substrates 600, 602 are pancakeshaped (in the sense that they are relatively large area compared totheir thickness) oriented vertically, and can each be relatively large(in surface area) and relatively thin (e.g. on the order of a fewmillimeters, and preferably not thicker than a meter). Each substratecan move (e.g. by a pulley or hydraulic system, not shown) between anupper position in which carbon dioxide laden air is brought into contactwith the medium carried by the substrate to remove carbon dioxide fromthe air, and a lower position in which process heat is directed at thesubstrate to remove carbon dioxide from the medium. The substrates 600,602 are porous with large surface areas, so that air directed at asubstrate can flow through the substrate. When a substrate is in anupper position (e.g. the position of substrate 600), carbon dioxideladen air is directed at the substrate (e.g. by a fan 604 shown indashed lines), so that as the air flows through the substrate, thecarbon dioxide contacts the medium and is substantially removed from theair. Thus, carbon dioxide laden air is directed at and through thesubstrate so that carbon dioxide comes into contact with the medium,carbon dioxide is substantially removed from the air by the medium, andair from which the carbon dioxide has been substantially removed isdirected away from the substrate. When a substrate is moved to the lowerposition (e.g. the position of substrate 602), process heat is directedat the substrate (e.g. via a fluid conduit 606), and carbon dioxide isremoved (drawn off) by a source of fluid that is directed at thesubstrate (in the direction shown by arrow 608) and a source of suction610 by which carbon dioxide that has been removed from the medium isdrawn away from the substrate. The substrates 600, 602 can alternativelymove between the upper and lower positions, so that the substrate in theupper position is removing carbon dioxide from the air and carbondioxide is being removed from the substrate in the lower position. Itshould be noted that rather than the fan, if there are strong windsavailable natural wind flows can be used to drive the air through thesubstrate. In addition, as described below, the fan can be replaced witha solar driven source (or by either wind or thermally-driven aircurrents), in which case the efficiency and cost reduction of extractionof carbon dioxide from atmospheric air can be further improved.Moreover, rather than switching the positions of the substrates, themeans for generating the air flows, the flow of process heat, and theflow of carbon dioxide away from the substrate can be switched as carbondioxide is captured from the air and then extracted from the medium, aswill be readily apparent to those in the art.

FIG. 7 is a schematic illustration of another version of a medium forremoving carbon dioxide from an atmosphere and for removing carbondioxide from the medium, according to the principles of the presentinvention. Specifically, in FIG. 7, a pair of substrates 700, 702 areillustrated, each of which can be the same medium as in FIG. 6, above,to remove carbon dioxide from the atmosphere. The substrates 700, 702are oriented horizontally, and can each be relatively large (in surfacearea) and relatively thin (e.g. on the order of millimeters orcentimeters, up to a meter). Each substrate can move horizontally (e.g.by a pulley system (not shown) between an air extraction position inwhich carbon dioxide laden air is brought into contact with the mediumcarried by the substrate to remove carbon dioxide from the air, and acarbon extraction position in which process heat is directed at thesubstrate to remove carbon dioxide from the medium. The substrates 700,702 are porous, so that air directed at a substrate can flow through thesubstrate. When a substrate is in an air extraction position (e.g. theposition of substrate 700), carbon dioxide laden air is directed at thesubstrate (e.g. by a fan 704 shown in dashed lines), so that as the airflows through the substrate, the carbon dioxide contacts the medium andis substantially removed from the air. Thus, carbon dioxide laden air isdirected at and through the substrate so that carbon dioxide comes intocontact with the medium, carbon dioxide is substantially removed fromthe air by the medium, and air from which the carbon dioxide has beensubstantially removed is directed away from the substrate. When asubstrate is moved to the carbon extraction position (e.g. the positionof substrate 702), process heat is directed at the substrate (e.g. via afluid conduit 706), and carbon dioxide is removed (drawn off) by asource of fluid that is directed at the substrate (in the directionshown by arrow 708) and a source of suction 710 by which carbon dioxidethat has been removed from the medium is drawn away from the substrate.The substrates 700, 702 can alternatively move between the airextraction and carbon extraction positions, so that the substrate in theair extraction position is removing carbon dioxide from the air andcarbon dioxide is being removed from the substrate in the carbonextraction position. It should be noted that rather than the fan, ifthere are strong winds available natural wind flows can be used to drivethe air through the substrate. In addition, as described below, the fancan be replaced with a solar driven source (or by either wind orthermally-driven air currents), in which case the efficiency and costreduction of extraction of carbon dioxide from atmospheric air can befurther improved. Moreover, rather than switching the positions of thesubstrates, the means for generating the air flows, the flow of processheat, and the flow of carbon dioxide away from the substrate can beswitched as carbon dioxide is captured from the air and then extractedfrom the medium, as will be readily apparent to those in the art.

The version of the invention shown in FIG. 9 is generally similar to thehorizontally oriented version of FIG. 7, but in the version of FIG. 9,rather than a fan being the source that moves the carbon laden airthrough the substrate in the air extraction position (e.g. substrate900), there is a source of gas flow that is generated from a solarheating tower or chimney (shown schematically at 912 in FIG. 9). A solarchimney can be generated by heating an air mass with the sun. The solarchimney would have a “skirt” (shown in dashed lines 913 in FIG. 9) thatenables the solar heated air to be concentrated in the chimney. Thus, asolar field with a solar chimney can be associated with a system andstructure that removes carbon dioxide from the atmosphere and removescarbon dioxide from a medium in the manner shown and described inconnection with FIG. 7. However, rather than a fan 704 as the primarydriver of carbon dioxide laden air at the substrate, the carbon dioxideladen air is heated by solar energy and that air is allowed to rise inthe solar funnel or tower 912. Because of the tendency for the hot airto rise, an upward draft is generated, that would carry with it carbondioxide laden air, and the substrate 900 would be positioned in the wayof that upward draft. Thus, the carbon dioxide laden air would bedirected through the substrate 900 in the air extraction position, andcarbon dioxide would be removed from the substrate 902 in the carbonextraction position in the same way as shown and described in connectionwith FIG. 7. By driving the extraction of carbon dioxide from air bysolar energy, the costs of extraction are further reduced, and theoverall operation is highly renewable. Of course, provision would needto be made for those periods when the sun didn't shine, and some form ofdriver similar to the fan 704 (FIG. 7) would be needed. But in any case,having periods in which, instead of the fan, replacing the fan with asolar driven source (or by either wind or thermally-driven aircurrents), the efficiency and cost reduction of extraction of carbondioxide from atmospheric air can be further improved.

FIG. 8 is a schematic illustration of yet another version of a mediumfor removing carbon dioxide from an atmosphere and for removing carbondioxide from the medium, according to the principles of the presentinvention. In FIG. 8, the medium from which carbon dioxide is removedfrom atmospheric air and from which carbon dioxide is removed from themedium is disposed on a continuously moving substrate composed, e.g., ofpellets laden with the sorbent 800. The substrate moves through an airextraction zone 814, where carbon dioxide laden air is directed at andthrough the substrate (which is also porous as with the priorembodiments) so that carbon dioxide is removed from the air. Thesubstrate 800 then moves to a carbon extraction zone 816, where processheat is directed at the substrate and carbon is drawn away from thesubstrate in the manner described above in connection with FIGS. 6, 7.Then, the substrate 800 moves to and through a heat exchange zone 818where the temperature of the substrate is lowered (e.g. by the air thatflowed through the substrate in the air extraction zone, and by anyadditional cooling device that may be useful in reducing the temperatureof the substrate to a level that enables it to efficiently remove carbondioxide from the air when the substrate moves back through theextraction zone 814. In addition, the system of FIG. 8 may have anothercarbon extraction zone 816, where process heat is directed at thesubstrate and carbon is drawn away from the substrate in the mannerdescribed above in connection with FIGS. 6, 7.

It should also be noted that in all of the versions of the inventiondescribed above, the removal of carbon dioxide from the air can be atleast partially performed under non equilibrium conditions.Additionally, it should be noted that applicants' preferred concept forextracting carbon dioxide from the atmosphere comprises using arelatively thin, large surface area substrate with a medium (e.g. anamine) that removes carbon dioxide from the atmosphere and using processheat to remove carbon dioxide from the medium. Using a relatively largearea substrate perpendicular to the direction of air flow isparticularly useful, because of the relatively low concentration ofcarbon dioxide in the atmosphere (as opposed to the relatively highconcentration that would normally be found, e.g. in flue gases).

New System, Components and Method Concepts for Removing Carbon Dioxidefrom Carbon Dioxide Laden Air, According to the Present Invention

Sorbent Structure and General Operation of Sorbent.

FIG. 12 is a schematic illustration of a cellular, ceramic substratestructure, of a type produced by Corning under the trademark Celcor®,that can be used in a sorbent structure, in accordance with theprinciples of the present invention. The sorbent (e.g. an amine) iscarried by (e.g. coated or otherwise immobilized on) the inside of oneor more of the Celcor®, cellular ceramic substrates, which provides ahigh surface area and low pressure drop, as CO₂ laden air flows throughthe substrate. The sorbent structure can comprise e.g., a plurality ofthe Celcor®, cellular, ceramic substrates or a single substrate, havingthe type of pancake shape described above in connection with FIG. 6(i.e. surface area much greater than thickness), and the CO₂ laden airis directed through the cells of the sorbent structure. It is alsocontemplated that the sorbent structure can be formed by embedding thesorbent material in the Celcor® cellular, ceramic structure to form amonolithic sorbent structure.

In addition, it should be noted that the substrate, while preferablyceramic, an inorganic material, can be an organic material.

CO₂ laden air is passed through the sorbent structure, which ispreferably pancake shaped, and the sorbent structure binds the CO₂ untilthe sorbent structure reaches a specified saturation level, or the CO₂level at the exit of the sorbent structure reaches a specified valuedenoting that CO₂ breakthrough has started (CO₂ breakthrough means thatthe sorbent structure is saturated enough with CO₂ that a significantamount of additional CO₂ is not being captured by the sorbentstructure). Systems for measuring CO₂ concentration are well-known.

When it is desired to remove and collect CO₂ from the sorbent structure(and regenerate the sorbent structure), in a manner described furtherbelow in connection with FIGS. 10a-h , the sorbent structure is removedfrom the carbon dioxide laden air stream and isolated from the airstream and from other sources of air ingress. Steam is then passedthrough the sorbent structure. The steam will initially condense andtransfer its latent heat of condensation to the sorbent structure.Eventually the sorbent structure will reach saturation temperature andthe steam will pass through the sorbent structure without condensing. Asthe condensate and then the steam pass through and heat the sorbentstructure the CO₂ that was captured by the sorbent structure will beliberated from the sorbent structure producing more condensed water inproviding the needed heat of reaction to liberate the CO₂ from thesorbent structure and be pushed out of the sorbent structure by thesteam or extracted by a fan/pump. Thus, the steam that is passed throughthe sorbent structure and releases the CO₂ from the sorbent, and forenergy efficiency cost reasons one would want to minimize the amount ofsteam used and that is mixed in with the CO₂. Thus, whatever is (or canbe) condensed upon exiting the regeneration chamber and the condensatecan be added to that generated in the regeneration chamber, and recycledto be heat and converted back into steam for use. This technique isreferred to as “steam stripping” and is also described further below.

Vertical Elevator Concept of FIGS. 10a-10f, and 10h

FIGS. 10a, 10b -1, 2 are schematic illustrations of structure and methodconcepts that further develop the principles by which carbon dioxide canbe removed from CO₂ laden air, according to the principles of thepresent invention. FIGS. 10c-h . FIGS. 10a and 10b -1, 2 differ in thatin FIG. 10a the Absorption Time is significantly greater thanRegeneration Time, but in FIG. 10b -1, 2, Absorption Time approximatelyequal to Regeneration Time.

Specifically, in FIG. 10a , a rectangular carbon dioxide capturestructure 1000 is illustrated, which has a sorbent structure, asdescribed herein, that can be brought into contact with CO₂ laden air toremove carbon dioxide from the CO₂ laden air. The rectangular carbondioxide capture medium is similar to the pancake shaped substrates ofFIG. 6, above. The improved carbon dioxide capture structure 1000comprises a top member 1002 that is preferably a solid metal plate, anda sorbent structure 1004 depending from the top member 1002, and held inplace by only vertical bars (for support) elsewhere, so that the sorbentmedium is open to the atmosphere on remaining four (4) sides. Thesupport is preferably formed of stainless steel. When located in astream of CO₂ laden air, the sorbent structure 1004 is open to CO₂ ladenair stream on the large area faces through which the air is directed bythe an or prevailing wind 2049 and carries the sorbent that binds tocarbon dioxide flowing through the sorbent structure, to capture carbondioxide from a flow of carbon dioxide laden air that is directed throughthe sorbent structure. The sorbent structure 1004 provides a highsurface area and low pressure drop, as CO₂ laden air flows through thesorbent structure 1004.

The carbon dioxide capture structure 1000 is supported for verticalmovement by an elevator structure, shown and described in overview inconnection with FIGS. 10a and 10b -1, 2, and whose details are furtherdescribed and shown in connection with FIGS. 10c-f and 10h . As shown inFIG. 10a , a hydraulic cylinder 1006 is connected via a piston and rods2034, 2059 with the top plate 1002 and the piston is moveable in astructural frame 1008 that protects the hydraulic cylinder from theambient environment. The hydraulic cylinder 1006 can selectively movethe carbon dioxide capture structure 1000 between a carbon dioxidecapture position that is in line with a flow of carbon dioxide laden air2024, 2049, and a regeneration position described further below. In thecarbon dioxide capture position, a flow of carbon dioxide laden air(labeled “fresh air inlet” in FIG. 10a ) is drawn through the carbondioxide capture structure 1000 (e.g. by means of an induced draftcreated by a fan 1010 driven by a motor 1012). The carbon dioxide ladenair flows through the sorbent support substrate 1004 where the sorbentbinds the carbon dioxide, to remove the carbon dioxide from the air, sothat the air that exits the carbon dioxide capture structure 1000 issubstantially depleted of carbon dioxide (preferably about 95% depletedof carbon dioxide).

The carbon dioxide capture structure 1000 can be selectively moved to aregeneration position (by the hydraulic cylinder 1006 or by a pulleysystem that would perform the analogous function), where carbon dioxideis separated from the sorbent structure 1004, to enable the carbondioxide to be collected and sequestered, and to enable the sorbentstructure to be regenerated, so that the sorbent structure can then bemoved back to a position where it is in line with a flow of carbondioxide laden air, to remove additional carbon dioxide from the air. Aregeneration box 1014 is located below the carbon dioxide capturestructure 1000. The regeneration box 1014 is preferably solid metalplate on 5 sides, and is open on top, so that when the carbon dioxidecapture structure 1000 is lowered into the box 1014, the top plate 1002will close the top of the regeneration box 1014, creating asubstantially air-tight mechanical seal with the top of the CO₂Regeneration Box.

The regeneration box 1014 is well insulated for heat conservationpurposes and can be selectively heated by a flow of process heat(preferably from a co-generation system and process, as describedfurther herein). As the regeneration box 1014 is heated (preferably bythe “steam stripping process described herein), the carbon dioxide isseparated from the sorbent structure, and is drawn off so that thecarbon dioxide can be sequestered. As the carbon dioxide is separatedfrom the sorbent structure, and drawn from the regeneration box 1014,the sorbent structure is regenerated, so that the carbon dioxide capturestructure 1000 can be moved to the position in which it is in line witha flow of carbon dioxide laden air, to remove carbon dioxide from thecarbon dioxide laden air.

FIG. 10b -1, 2 schematically illustrates an alternative to the structureand technique of FIG. 10a , in that a pair of carbon dioxide capturestructures 1000 are provided, each of which is configured in accordancewith the carbon dioxide capture structure of FIG. 10a , and each ofwhich is moved by a hydraulic cylinder 1002 between a carbon captureposition in which the carbon capture structure is in line with a flow ofcarbon laden air, and a regeneration position in which the carbondioxide capture structure is lowered into a regeneration box 1014 thatis configured like, and operates in a similar manner to, theregeneration box 1014 of FIG. 10a . The only essential different betweenthe carbon capture structure and technique of FIG. 10b -1, 2 and FIG.10b -1, 2, is that in FIG. 10b -1, 2, one carbon dioxide capturestructure can always be in line with a flow of carbon dioxide laden airwhile the other carbon dioxide capture structure is being regenerated inthe manner described above in connection with FIG. 10a . Thus, in FIG.10b -1, 2 (and in a manner similar to that shown in FIG. 6), when afirst carbon dioxide capture structure 1000 is in an upper position(e.g. the upper position shown in FIG. 10b -1, 2), carbon dioxide ladenair is directed through a sorbent structure, so that the sorbentstructure binds carbon dioxide in the carbon dioxide laden air. When thefirst carbon dioxide capture structure 1000 is moved to the lowerposition and into the regeneration box 1014, process heat is directed atthe substrate, and carbon dioxide is removed (drawn off) the sorbentsupport structure (again preferably by the “steam stripping” processdescribed herein). The pair of carbon dioxide capture structures 1000can alternatively move between the upper and lower positions, so thatthe carbon dioxide capture structure in the upper position is removingcarbon dioxide from the carbon dioxide laden air and carbon dioxide isbeing removed from the sorbent structure that is in the lower position.

While FIGS. 10a and 10b -1, 2 each shows a single sorbent structure forremoving carbon dioxide from carbon dioxide laden air and forregenerating a carbon dioxide sorbent structure (such sorbent structuresometimes referred to herein as a Unit, in practice a global thermostatsystem would have a number of Units, each of which is configured andoperates in accordance with the structures and techniques describedabove, as will be clear to those in the art. Moreover, FIG. 10h showsand describes the elevator structure in additional detail, and as shownin FIGS. 10 c, d, e and f, the elevator structure can comprise, e.g.,pairs of hydraulic cylinders that are located such that they do notinterfere with the flow of carbon dioxide laden air through the sorbentstructure.

Moreover, the following additional features of the structures andtechniques of FIGS. 10a and 10b -1, 2 should also be noted.

-   -   a. Piping, valves, etc. For the Low Level Process Heat        Source/Supply Header 2029 (typically Pressure Steam), which will        most likely be a horizontal pipe rack run located underneath the        horizontal row of identical Global Thermostat (GT) Units,        running parallel with the “Dimension W” 2044 shown in FIGS. 10a,        10b -1, 2. If the number of Global Thermostat (GT) Units is also        expanded vertically upward, by building a structure with        additional platform levels at the appropriate elevations, there        will also be a vertical header, or vertical pipe rack run,        located at the very end of the horizontal row of identical GT        Units, adjacent to the structure containing the additional        platform levels at the appropriate elevations.    -   b. Piping, valves, etc. For the Low Level Process Heat Return        Header 2027 (typically Low Pressure Steam Condensate), which        will most likely be a horizontal pipe rack n located underneath        the horizontal row of identical Global Thermostat (GT) Units,        running parallel with the “Dimension W” shown in FIGS. 10a, 10b        -1, 2. If the number of Global Thermostat (GT) Units is also        expanded vertically upward, by building a structure with        additional platform levels at the appropriate elevations, there        will also be a vertical header, or vertical pipe rack run,        located at the very end of the horizontal row of identical GT        Units, adjacent to the structure containing the additional        platform levels at the appropriate elevations.    -   c. Piping, valves, etc. For the optional Cooling Water Supply        (CWS) Header 2030, which will most likely be a horizontal pipe        rack run located underneath the horizontal row of identical        Global Thermostat (GT) Units, running parallel with the        “Dimension W” shown in FIGS. 10a, 10b -1, 2. If the number of        Global Thermostat (GT) Units is also expanded vertically upward,        by building a structure with additional platform levels at the        appropriate elevations, there will also be a vertical header, or        vertical pipe rack run, located at the very end of the        horizontal row of identical GT Units, adjacent to the structure        containing the additional platform levels at the appropriate        elevations.    -   d. Piping, valves, etc. for the optional Cooling Water Return        (CWR) Header 2028, which will most likely be a horizontal pipe        rack run located underneath the horizontal row of identical        Global Thermostat (GT) Units, running parallel with the        “Dimension W” shown in FIGS. 10a, 10b -1, 2. If the number of        Global Thermostat (GT) Units is also expanded vertically upward,        by building a structure with additional platform levels at the        appropriate elevations, there will also be a vertical header, or        vertical pipe rack run, located at the very end of the        horizontal row of identical GT Units, adjacent to the structure        containing the additional platform levels at the appropriate        elevations.    -   e. Piping, valves, etc. For the CO₂ (>95.00 mole %) to CO₂        Product Storage Header 2026, which will most likely be a        horizontal pipe rack run located underneath the horizontal row        of identical Global Thermostat (GT) Units, running parallel with        the “Dimension W” shown in FIGS. 10a, 10b -1, 2. If the number        of Global Thermostat (GT) Units is also expanded vertically        upward, by building a structure with additional platform levels        at the appropriate elevations, there will also be a vertical        header, or vertical pipe rack run, located at the very end of        the horizontal row of identical GT Units, adjacent to the        structure containing the additional platform levels at the        appropriate elevations.    -   (f) The CO₂ Receiving/Storage Vessel 2026, and any and all        equipment required to connect to, or tie-in to, a high pressure        CO₂ disposal pipeline.    -   g. Supply and Return tie-ins (piping, valves, etc.) 2029 to the        Low Level Process Heat Source at the existing industrial        facility (Power Plant, Chemical Plant, or Refinery, etc.), which        would most likely be ordinary low pressure steam supply/low        pressure steam condensate return 2027.    -   h. Supply and Return tie-ins (piping, valves, etc.) to the Low        Level Cooling Source at the existing industrial facility (Power        Plant, Chemical Plant, or Refinery, etc.), which would most        likely be ordinary or common cooling water supply (CWS)/cooling        water return (CWR) 2030/2028.    -   i. All instrumentation, all electrical facilities (such as        substations, wiring, etc.), all general utility connections        (such as instrument air, potable water, etc.), all safety and        shutdown systems, etc. This would also include a Control House,        with a typical Computer Data Logger/Computer Control System.    -   j. All of the block valves shown in FIGS. 10a, 10b -1, 2 will be        specified to be either “minimal leakage” or TSO (tight shut-off)        block valves, whichever is most practical or most feasible.    -   k. All of the block valves shown FIGS. 10a, 10b -1, 2 will be        fully automated block valves (either motorized, hydraulically,        or pneumatically operated). All of these block valves will be        interlocked together by a timer/sequencer system that is        computer controlled. The Hydraulic Fluid Pump(s) and the CO₂        Product/Recycle Gas Blower(s) will also be connected to, and        interlocked by, the timer/sequencer system that is computer        controlled.    -   l. While the preferred sorbent structure described herein        comprises a sorbent material (i.e. an amine) that is carried by        (e.g. coated or otherwise immobilized on) the inside of Celcor®        cellular substrate, it is contemplated that the sorbent        structure can also be formed by embedding the sorbent material        in the Celcor® cellular structure to form a monolithic sorbent        structure.    -   m. It is recognized that it may be important to remove oxygen        from the environment about the hot sorbent structure, both        before and after regeneration of the sorbent structure, to avoid        oxygen contamination of the sorbent structure (which would        result from oxygen poisoning the sorbent structure by oxidizing        the sorbent structure). The manner in which removal of oxygen        can be handled is described below in connection with a technique        referred to as “steam stripping with purge gas”.        Steam Stripping

There are 2 techniques that are contemplated for the steam strippingprocess. One technique is referred to as “steam stripping with steamonly”. The other technique is referred to as “steam stripping with purgegas”. Both techniques utilize system components and process steps thatare schematically shown in FIG. 10 g.

The technique referred to as “steam stripping with steam only” works inthe following way:

-   -   a. Air is passed through the channels in the sorbent structure        and the CO₂ is removed from the air by the sorbent structure        until the sorbent structure reaches a specified saturation level        or the CO₂ level at the exit of the sorbent structure reaches a        specified value denoting that CO₂ breakthrough has started, or        for a specified time period determined by testing.    -   b. The sorbent structure is removed from the air stream and        isolated from the air flow and from air ingress and CO₂        migration to the outside air, when placed in its CO₂ removal        position 2105.    -   c. Low pressure steam 2100 is passed through the channels in the        sorbent structure 2105. The steam will initially condense and        transfer its latent heat of condensation to the sorbent        structure in the front part of the sorbent structure. The heat        of condensation raises the temperature of the sorbent structure        and provides energy to drive the CO₂ desorption process from the        sorbent structure. Eventually the front part of the sorbent        structure will reach saturation temperature and the liberated        CO₂ will be pushed out by the steam or extracted by a fan. This        process will move deeper into the sorbent structure from the        front part of the sorbent structure where the steam enters until        the CO₂ is liberated (note the fraction released will depend        upon the sorbent structure and temperature of the steam used).        Only an adequate amount of steam will be provided to achieve        desorption of the CO₂ from the sorbent structure so as to        minimize the steam used and minimize the amount of steam mixed        in with the liberated CO₂). As the condensate and then the steam        pass through the sorbent structure and heat the sorbent, the CO₂        will be liberated from the sorbent structure and be transferred        into the steam and condensate. The condensate will have a        limited ability to “hold” the CO₂ and once saturated the “sour”        water will not hold any more CO₂ and the CO₂ will remain in the        vapor phase as it is pushed out by the steam or extracted with a        fan. Once the steam has passed through the sorbent structure it        has to be condensed to liberate the CO₂. This is achieved in the        condenser 2106 which uses cooling water 2108 to remove the heat.        The collected stream will have some steam mixed in that will be        minimized to the extent possible, and that steam has to be        condensed to separate it from the CO₂. Alternatively the steam        could be condensed, using heat loss to the atmosphere, in an        uninsulated pipe or a finned pipe. This heat is a loss to the        system although an alternative would be to use the air exiting        the sorbent structure in the adsorption step (Step 1 above) to        condense the steam. This would raise the temperature of the air        at the exit of the sorbent structure and provide an additional        driving force to move the air through the sorbent structure and        reduce the energy requirements.    -   d. Once the sorbent structure has had the CO₂ removed then the        sorbent structure is raised up back into the air stream. The air        will cool the sorbent structure and remove any remaining        moisture. The sorbent structure will then remove the CO₂ until        the specified breakthrough occurs (see Step 1) and the sorbent        structure is then lowered into the regeneration position and the        process repeated.    -   e. The condensate from the desorption process (removing the CO₂        from the sorbent structure) contains CO₂ at saturation levels.        This condensate 2109 will be close to saturation temperature (as        only sufficient steam is added to the system to achieve CO₂        removal) and is recycled to a boiler where low pressure steam        from a facility (petrochemical plant or utility power plant) is        used to regenerate the steam 2098 used for heating the sorbent        structure. The re-use of the CO₂ saturated steam eliminates the        requirement to treat large quantities of acidic water.

The technique referred to as “steam stripping with purge gas” works inthe following way:

-   -   a. Air is passed through the channels in the sorbent structure        and the CO₂ is removed from the air by the sorbent structure        until the sorbent structure reaches a specified saturation level        or the CO₂ level at the exit of the sorbent structure reaches a        specified value denoting that CO₂ breakthrough has started, or        for a specified time period determined by testing.    -   b. The sorbent structure is removed from the air stream and        isolated from the air flow and from air ingress and CO₂        migration to the outside air.    -   c. In order to remove oxygen from the channels in the sorbent        structure a purge of inert gas is passed through the sorbent        structure for a short time period.    -   d. Low pressure steam is passed through the channels in the        sorbent structure. The steam will initially condense and        transfer its latent heat of condensation to the sorbent        structure in the front part of the sorbent structure. The heat        of condensation raises the temperature of the sorbent structure        and provides energy to drive the CO₂ desorption process from the        sorbent structure. Eventually the front part of the sorbent        structure will reach saturation temperature and the liberated        CO₂ will be pushed out by the steam or extracted by a fan. This        process will move deeper into the sorbent structure from the        front part of the sorbent structure here the steam enters until        the CO₂ is liberated (not the fraction released will depend upon        the sorbent structure and temperature steam used). Only an        adequate amount of steam will be provided to achieve desorption        of the CO₂ from the sorbent structure so as to minimize the        steam used and minimize the amount of steam mixed in with the        liberated CO₂). As the condensate and then the steam pass        through the sorbent structure and heat the sorbent the CO₂ will        be liberated from the sorbent structure and be transferred into        the steam and condensate. The condensate will have a limited        ability to “hold” the CO₂ and once saturated the “sour” water        will not hold any more CO₂ and the CO₂ will remain in the vapor        phase as it is pushed out by the steam or extracted with a fan.        One the steam has passed through the sorbent structure it has to        be condensed to liberate the CO₂. This is achieved in the        condenser 2106 which uses cooling water to remove the heat. The        collected stream will have some steam mixed in that will be        minimized to the extent possible, and that steam has to be        condensed to separate it from the CO₂. Alternatively the steam        could be condensed, using heat loss to the atmosphere, in an        uninsulated pipe or a finned pipe. This heat is a loss to the        system although an alternative would be to use the air exiting        the sorbent structure in the adsorption step (Step 1 above) to        condense the steam. This would raise the temperature of the air        at the exit of the sorbent structure and provide an additional        driving force to move the air through the sorbent structure and        reduce the energy requirements.    -   e. In order to cool the sorbent structure before it is replaced        in the air stream an inert gas is passed through the sorbent        structure until it is cooled to a specified temperature so that        damage to the sorbent structure will not occur when it is placed        back into the air stream.    -   f. Once the sorbent has had the CO₂ removed and the sorbent        structure cooled then the sorbent structure is raised up back        into the air stream. The air will continue to cool the sorbent        structure and remove any remaining moisture. The sorbent        structure will then remove the CO₂ until the specified        breakthrough occurs (see Step 1) and the sorbent structure is        then lowered into the regeneration position and the process        repeated.    -   e. The condensate from the desorption process (removing the CO₂        from the sorbent structure) contains CO₂ at saturation levels.        This condensate will be close to saturation temperature (as only        sufficient steam is added to the system to achieve CO₂ removal)        and is recycled to a boiler 2100 where low pressure steam from a        facility (petrochemical plant or utility power plant) is used to        regenerate the steam used for heating the sorbent structure. The        re-use of the CO₂ saturated steam eliminates the requirement to        treat large quantities of acidic water.

It should be noted that in each of the steam stripping techniquesdescribed above, there are two closed steam loops connected by a heatexchanger. One steam loop supplies the process heat and returns to theboiler hot condensate that results from heating the loop that does thesteam stripping. The other steam loop is the steam loop that does thesteam stripping and regeneration of the sorbent structure.

Steam stripping, as described above, would be performed in the foregoingmanner while the sorbent structure is disposed in the regeneration box1014 shown and described in connection with FIGS. 10a, 10b -1, 2. Oncethe sorbent structure has had the CO₂ removed then the sorbent structureis raised from the regeneration box 1014 back into the carbon dioxideladen air stream, as also shown and described in connection with FIGS.10a, 10b -1, 2. The carbon dioxide laden air stream will cool thesorbent structure and remove any remaining moisture. The sorbentstructure will then remove the CO₂ until the specified breakthroughoccurs and the sorbent structure is then lowered into the regenerationposition in regeneration box 1014.

Sorbent Coated Pellet Structure and Come of FIGS. 11a , 11 b

FIGS. 11a, and 11b show 2 examples of another structure and techniquefor removing carbon dioxide from a flow of carbon dioxide laden air, andregenerate a sorbent used to absorb or bind to the carbon dioxide, inaccordance with the principles of the present invention.

In the structures and techniques of FIGS. 11a and 11b , particles,preferably of pellet size, flow by gravity into a pellet feedsource/storage bin 1100. The pellets are coated with the sorbent (e.g.an amine) that absorbs or binds carbon dioxide in a flow of carbondioxide laden air that flows through the pellets. The pellets can beselectively fed through a valve structure 1102 into an air contactingvessel 1104, and a flow of carbon dioxide laden air is directed throughthe vessel 1104, so that the sorbent absorbs or binds the carbon dioxideand removes the carbon dioxide from the air. A regeneration bin 1106 isprovided below the air contacting vessel 1104. The pellets can beselectively directed into the regeneration bin 1106, where process heatis directed at the pellets, to remove carbon dioxide from the sorbentand regenerate the sorbent. The pellets with the regenerated sorbent arethen directed to a vertical lifting structure 1108, where they areredirected to a location that enables them to flow into the feedsource/storage bin 1100 continue the carbon dioxide removal process. Thevertical lifting structure 1108 can comprise, e.g. an air blownstructure, an elevator, a screw conveyer, etc, that directs the pelletsback to the location that enables them to restart the carbon dioxideremoval process. The difference between the systems and techniques ofFIGS. 11a and 11b is that in the system and technique of FIG. 11a , thecarbon dioxide laden air flows downward through a mass of pelletscontained in the air contacting vessel 1104, whereas in the system andtechnique of FIG. 11b , the carbon dioxide laden air flows horizontallythrough the pellets are then are flowing into the air contacting vessel1104.

The structure and techniques of FIGS. 11a, 11b are useful in removingcarbon dioxide from carbon dioxide laden air, and may also be useful inremoving carbon dioxide from flue gases that emanate from a source thatwould otherwise direct carbon dioxide into the atmosphere. Specifically,the structure and techniques of FIGS. 11a and 11b can be used to providesorbent coated pellets directly in the path of flue gases that emanatefrom a source and would otherwise be directed into the atmosphere. Thesorbent coated pellets can be used to remove carbon dioxide from theflue gases, and the sorbent can then be treated with process heat, toremove the carbon dioxide from the pellets (so that it can be drawn offand sequestered), and to regenerate the sorbent on the pellets (so thatit can continued to be used to remove carbon dioxide from the fluegases).

It should also be noted that while the structures of FIGS. 11a, 11b arevertically oriented, it may be desirable that certain structures (e.g.the particle beds) be tilted (to facilitate water that condenses fromsteam during regeneration to drop to the bottom of the particle bed andnot block the particle beds), or even oriented horizontally (also todeal with the condensed water issue).

Summary of the Further Embodiments of the Present Invention

The present invention further teaches systems, components and methodscapable of capturing carbon dioxide from ambient air alone, or from amixture of ambient air and a relatively small percentage offlue-originating gases. The term “ambient air”, as used in thisspecification, means and includes unenclosed air under the conditionsand concentrations of materials present in the atmosphere at aparticular location.

The further improvement of the present invention provides a system andmethod for removing carbon dioxide from the ambient atmosphere bydirecting the CO₂-laden ambient air through a porous sorbent structurethat selectively removably binds (captures) CO₂, preferably underambient conditions, and removing (stripping) CO₂ from the sorbentstructure (and thereby effectively regenerating the sorbent structure)by using process heat, preferably in the form of low temperature steam,at a temperature preferably of not greater than 120° C. to heat thesorbent structure and to strip off the CO₂ from the sorbent structure,and most preferably using steam as the heat carrier. The sorbentstructure is preferably a porous solid substrate holding on its surfacesamine binding sites for CO₂.

According to the present invention, air, alone or mixed in an air/flue“blender” is conducted to and into contact with a sorbent, the sorbentis preferably alternately moved between carbon dioxide capture andregeneration positions. After the step of carbon dioxide capture, thesorbent is moved to a “stripping” regeneration position, where steamco-generated by means of the process heat is used to “strip” the carbondioxide from the sorbent, whereupon the capturing and regenerationcycles are repeated.

The unexpected advantage of capturing CO₂ at ambient temperatures ismade possible by the unexpected effectiveness of steam stripping the CO₂from the sorbent structure using process heat, specifically using steamat atmospheric pressure. Further the reason that such low temperaturesteam may be used is the mechanism of the steam. As the steam frontproceeds into and through the sorbent structure, it gradually heats thestructure as the steam condenses. Behind the steam front one will have alow partial pressure of CO₂, as a result of the presence of steam, whichwill encourage more CO₂ to be stripped off. Thus, the steam isfunctioning behind the steam front as a sweep, or purge, gas. That is,in front the steam is driving off the CO₂ by heat, and behind by partialpressure dilution.

In accordance with one embodiment of this invention, the CO₂-capturingsorbent structure preferably comprises a monolith with (highly) porouswalls (skeleton) that contains amine binding sites which selectivelybind to CO₂. In another embodiment, the monolith has porous walls(substrate) and upon the surfaces, or in the pores, of which isdeposited an amine group-containing material which selectively binds tothe CO₂. In another embodiment, the monolithic highly porous skeletonhas deposited on its surfaces a coating of a highly porous substrateformed of a material that selectively supports the amine-groupcontaining material.

In yet another embodiment of this invention, the amine-group containingmaterial is carried by a substrate, in the form of relatively smallsolid particles, including as both a stationary and a moving bed.

In yet another preferred embodiment, the substrate itself is formed of apolymerized amine-containing skeleton. Most preferably, under conditionsmet in most countries, the amine sorbent is a polymer having onlyprimary amine groups, i.e., the nitrogen atom is connected to twohydrogen atoms. However, where ambient conditions are at an extremelylow temperature, e.g., less than 0° C., as may be found in most parts ofAlaska, or Northern Scandinavia or Asia, it is believed that weakerbinding secondary and tertiary amines can be effective, as they are forhigh concentration flue gas.

The present invention is designed to capture carbon dioxide from theatmosphere under ambient conditions. Ambient conditions includesubstantially atmospheric pressure and temperatures in the range of fromabout − (minus) 20° C. to about 35° C. It will be appreciated thatambient air has no fixed CO₂ concentration.

The captured CO₂ is preferably stripped from the sorbent using processheat in the form of saturated steam, thus regenerating the sorbent. Thesaturated steam is preferably at a pressure of substantially at or nearatmospheric pressure and a temperature of close to 100° C., i.e., up toabout 130° C., with 105-120° C. being a preferred range. It should alsobe noted that the temperature of the incoming steam should besuperheated at the pressure it is fed to the present process, i.e., at ahigher temperature than would be the equilibrium temperature at thepressure of the sorbent structure, in the regeneration chamber. Afterthe CO₂ is stripped from the sorbent, it can then be readily separatedfrom the steam by the condensation of the steam and removal of the CO₂.The condensed, still hot water, and any steam is recycled to the processsteam generator to save the sensible heat energy. The CO₂ lean air isexhausted back to the outside (ambient) air.

Moreover, in yet another of its aspects, this invention is preferablycarried out immediately adjacent to a carbon fuel-using industrial site,burning a carbon-containing fuel to provide heat and power to the site,and wherein a small percentage, preferably not more than about 5% byvolume, and most preferably between about 1 and 3% by volume, of tgasfrom the fuel burning, is mixed with the air before it is directed overthe surfaces of the sorbent.

In yet another embodiment, up to about 25% by volume of an effluent gascan be added to the air. As before, it is important that the mixing waslimited to a CO₂ concentration at which the rate of CO₂ capture was nothigh enough that the exothermic heat released during adsorption wouldraise the temperature of the monolith loaded with the sorbent to thepoint that its effectiveness for capturing CO₂ was diminished. It mustbe noted that the term “effluent” gas can include a true flue gas, i.e.,from the combustion of hydrocarbon, such as fossil, fuels. However, theeffluent gas can also be the effluent from a hydrocarbon fuel generationprocess, such as the IGCC process of coal gasification, or more broadlyany exhaust from a power generation system based upon the combustion ofa hydrocarbon or any process operated at a high temperature created bythe oxidation of a hydrocarbon.

The fraction of the CO₂ captured depends upon the temperature in a waygiven by the Langmuir isotherm, which for the available primary aminesorbent is exponential with temperature because of its high heat ofreaction, i.e., about 84 kj/mole. A temperature increase from 25° C. to35° C. reduces the percent of amine sites that can capture CO₂ inequilibrium by about e⁻¹. Of course, in cold climates this will be aless serious constraint. For example, if the ambient temperature is 15°C., a rise of 10° C. would yield the same performance as the 25° C.case. The Langmuir isotherm for a primary amine is close to optimal atabout 15° C. in terms of the fraction of amine sites in equilibrium andthe sensible heat needed to collect CO₂, and regenerate the sorbenteffectively at about 100° C. A conceptual design is shown, where theeffluent gas is mixed with the air through a carburetor type ofapparatus, and the temperature rise is analyzed, in FIG. 27.

By combining with a CCS process effluent, many of the problemsassociated with directly mixing the effluent gas are avoided or at leastminimized, especially at proportions greater than 5%. Such problems withdirect injection of effluent gas include the high temperature of theeffluent gas, which creates several problems: The amount of effluent gasto be added to air is relatively small (not more than 25% by weight).The air stream and the effluent gas stream are both at low pressure andso there is, effectively, no energy in these streams that can be usedfor mixing without increasing the pressure drop. The air stream couldvary in temperature (depending upon the location of the plant) between−30° F. to +110° F. The high temperature has an effect upon thevolumetric flow and the power required for the fan. A low airtemperature could impact the process as effluent gas contains asignificant amount of water and has a dew point range between 120° F.and 145° F., depending upon the type of fuel, excess air rates, moisturecontent of the combustion air, impurities, etc. Thus, if the effluentgas is not mixed well with the air or the effluent gas ducting iscontacted by cold ambient air, condensation may occur. Effluent gascondensate is corrosive and its presence may result in damage to piping,ducting or equipment unless suitable materials of construction are used.

In addition, effluent gas can contain solid particles (even downstreamof filters or bag houses) that could, over time, block the smallpassages proposed for the substrate. Thus particular care must be takento understand the potential for such blockage by particulates duringnormal operation. Finally, other contaminants such as sulfur oxides, inthe flue gas that could deactivate the sorbent, in addition to beingcorrosive to the equipment.

Most of these problems are avoided when the system of this invention,including the use of a carburetor as described herein, by integratingthis system into a flue gas scrubbing process, such as the well-knownCCS process, such that the effluent gas from the flue gas CCS process isused in the system and process of this invention.

Combining this process with the CCS process, also improves overallcosts. As is well known, the incremental cost per tonne of CO₂ removalincreases as one increases the percent CO₂ removed, and becomes verycostly as one goes from 90% to 95% removal rate. As one reduces thepercent captured below a certain level, it also becomes more costly,either because the penalty for the CO₂ not captured increases insituations where CO₂ emissions are regulated and/or that the sourceremains a significant CO₂ emitter reducing the value of the wholeprocess. For these reasons the target for the effluent gas from the CCSprocess is usually 90% removal. On the other hand, costs of the presentinvention go down as the percent of CO₂ in the process stream increasesthrough the addition of the effluent gas to the air, as long as theconcentration of CO₂ remains below that where the temperature rise fromthe exothermic capture decreases the effectiveness of the sorbent.

When this process is integrated with a CCS process, such that thecarburetor system is used to mix the air with the effluent of the CCSprocess, instead of directly with the flue gas itself. There is anoptimum point, from a cost per tonne CO₂, for the CCS stage. Forexample, if the CCS process removes only 80% of the CO₂ from the fluegas, and passes the effluent from the CCS stage to the present aircapture step, mixing the remaining CO₂ (if 10% CO₂ in the flue gas, atan 80% removal, leaves 2% in the effluent from the CCS stage). In thatcase, if one mixed the 2% CO₂ stream into the air input to the presentinvention, for every 1% of that effluent stream mixed into the air onewould increase the CO₂ concentration input into the system of thisinvention by about 50%. The associated temperature rises can bedetermined for this embodiment, with the temperature rise depending onthe rate of CO₂ adsorption and thus the incident concentration of CO₂ inthe mixed process stream initially contacting the sorbent.

As another example, if one mixed in 5% effluent, costs would be reducedby a factor of 3; the concentration would be 3 times higher in the mixedstream than in the air alone, over a stand-alone air capture process.The temperature rise for that case is close to the 1% methane case formixing the full effluent gas stream version of the carburetor, or about3.5 degrees C. Most importantly, even if the air capture only removed70% of the CO₂ in the mixed stream, the combined processes (i.e., theCCS and the present process) would remove over 100% of the CO₂ emittedby the power plant. The combined result would be to produce carbondioxide free power, or other processes that used fossil fuel as theenergy source. The combined cost would be less than the cost ofattempting to do it all in one stage, by optimizing the portions of CO₂removed at each stage.

Besides achieving direct benefits from reducing the cost per tonne ofCO₂ collected, by optimizing the cost of each of the CCS process and theCO₂ process of the present invention, there are also other benefits fromsuch process integration. They include that the exhaust stream from theinitial flue gas processing is clean of particulates and otherimpurities, removing that problem/cost of cleaning the flue gas prior tocarrying out the present invention, further optimizing efficiency andlowering the cost of energy. There are many different precombustion andpost combustion CO₂ removal processes being pursued and new ones couldwell emerge in the future. The details of the amount mixed and possibleadditional processing of the exhaust from the first flue gas processingstage will vary in detail but the basic concept remains the same:cleaning and partially removing the CO₂ from the flue gas, or morebroadly “effluent” and then completing the CO₂ removal in the process ofthe present invention mixed with a larger quantity of air.

Detailed Description of the Further Embodiments of this Invention

Referring to the generalized block diagram of the process of the presentinvention shown in FIG. 16, Stage 1 provides for moving a flowing massof ambient air having the usual relatively low concentration of CO₂ inthe atmosphere, with a relatively low pressure drop (in the range of100-1000) pascals. The flow of CO₂ containing air from Stage 1, ispassed, in Stage 2, through a large area bed, or beds, of sorbent forthe CO₂, the bed having a high porosity and on the walls defining thepores a highly active CO₂ adsorbent, i.e., where the adsorption resultsin a relatively high Heat of Reaction.

Such a highly active CO₂ sorbent is preferably a primary aminegroup-containing material, which may also have some secondary aminegroups present. The primary amine groups are generally more effective atusual ambient temperatures in the range of from about 10-25° C. Byutilizing all primary amine groups, especially in the form of polymers,one can maximize the loading. The relatively low concentration of CO₂ inthe air (as opposed to effluent gases), requires a strong sorbent.Primary amines have a heat of reaction of 84 Kj/mole of CO₂ thatindicates stronger bonds, while the secondary amines only have a heat ofreaction of 73 Kj/mole. Note that at lower temperature −10 to +10° C.secondary amines could also be effective.

More generally, it should be noted that, broadly, the present inventionis based not only on the effectiveness of the primary amines underambient conditions, but also on the recognition that removing CO₂ fromair under ambient conditions is practical, as long as the stripping ofthe CO₂ from the sorbent is equally practical at relatively towtemperatures. Thus, this invention contemplates the use of othersorbents having the desirable properties of the primary amines withrespect to the air capture of CO₂; such sorbents would be used in theinvention of the process described in this application.

The primary amines work effectively at air capture (from atmosphericair) concentrations under ambient conditions. The loading of CO₂ dependsstrongly upon the ratio of the heat of reaction/K (boltzmann constant) T(temperature); the heat of reaction difference between primary andsecondary amines, as shown above, can cause a factor of about 100 timesdifference in loading, following the well known langmuir isothermequation. The amine groups are preferably supported upon a highly porousskeleton, which has a high affinity to the amines or upon which, or inwhich, the amines can be deposited.

Alternatively, the amine groups may be part of a polymer that itselfforms the highly porous skeleton structure. A highly porous aluminastructure is very effective when used as the skeleton to support theamines. This ceramic skeleton has a pore volume and surface to achievehigh loadings of amines in mmoles of amine nitrogen sites per gram ofporous material substrate. A preferred such skeleton support materialhas 230 cells per cubic inch with a thickness of six inches. Anotherstructure that can be used is based upon a silica porous material knownas cordierite and is manufactured and sold by Corning under thetrademark CELCOR. CELCOR product is made with straight macro channelsextending through the monolith, and the interior walls of the channelsare coated with a coating of porous material, such as alumina, into thepores of which the amine can be attached or deposited (and whichpreferably is adherent to the amine compounds).

The cost of the process can be reduced by making the monolith thinner,by increasing the density of primary amine groups per volume and thusrequiring less monolith volume to achieve an adsorption time larger thanthe time to move the bed between adsorption and regeneration and tocarry out the steam stripping. This can be achieved by utilizing amonolith contactor skeleton that is made out of a primary amine-basedpolymer itself, but is also at least partially achieved by forming thestructure of the monolith of alumina. Although alumina does not form asstructurally durable a structure as does cordierite, for the conditionsmet at the ambient temperature of the air capture or the relatively lowtemperatures at which the CO₂ adsorbed on the amities at ambienttemperatures can be stripped off, the structural strength of alumina isadequate.

The foregoing modifications are important for air capture because theyminimize the cost of making the structure as well as the amount ofenergy needed to heat the amine support structure up to the strippingtemperature.

It is also useful to provide relatively thin contactors, with highloading capacity for CO₂ with rapid cycling between adsorption andregeneration. This would use the tandem two bed version with oneadsorbing and the other regenerating. Utilizing flat pancake-like beds,having a length, in the direction of the air flow, in the range of notgreater than about 20 inches, to about 0.03 inch, or even thinner, ispreferred. The more preferred range of thickness is from not greaterthan about 8 inches, and most preferably not thicker than about 3inches.

When using the alumina coated CELCOR cordierite, or any monolithstructure provided with channels passing the full thickness of themonolith, the length of the contactor in the direction of air flow, fora fixed pressure drop and fixed laminar air flow, and with a fixed voidfraction, scales like the area of the individual square_channel openingsin the CELCOR monolith; and the cycle time, as determined by the sorbentbecoming_saturated with CO₂ or to some fixed level of CO₂ sorption,scales with the same factor. The void fraction is the ratio of openinput area to total input area of the front face of the monolith, facingthe air flow. Preferably, the void fraction of the monolith is between0.7 and 0.9, i.e., between 70% and 90% open channels.

Thus as one decreases the size of the individual monolith openings for afixed void fraction, the channel length, i.e., thickness of the monolithstructure for a fixed pressure drop, will decrease proportional to thearea of that opening, while the adsorption time to reach a fixed levelof adsorption, or to reach saturation, will decrease proportionally atthe same rate that the length decreases. Since the cost will decrease asthe length decreases (the shorter the device, the lower the cost,roughly proportional to length), limited by the extra cost that mayresult as one shortens the cycle time and the cost to make thinnerwalled monoliths. How far one can go in reducing the length will also belimited by the loading of so bent, e.g., the number of amine groups thatone can place in the pores of the walls, per unit volume of the monolithwalls, the higher the loading, the shorter one can make the length ofthe monolith, for a fixed cycle time.

-   -   The above parameters assume that a certain constant loading (of        sorbent groups, e.g., primary amine groups) is achieved. In        addition, the velocity of the air coming in was assumed constant        in the comments above. It must be understood that the pressure        drop per tonne of CO₂ capture increases as the velocity of the        air flow increases, which increases the cost of the electricity        to move the air, to the extent natural forces, such as the wind,        are not sufficient to achieve the desired airflow. The cost of        the whole process other than the electricity cost decreases as        the airflow velocity increases. Thus, the air velocity choice is        a compromise between capital cost, which is reduced as the        airflow velocity increases, and operating costs, that increase        as the airflow velocity increases. It is preferred to operate        with an incoming airflow in the range of 2-4 m/sec. The relative        costs will vary depending upon the local conditions at each        plant site, e.g. is there a dependable prevail wind present or        not and the local cost of electricity.

It has further been found that the CO₂ capture time can be several timeslonger than the CO₂ stripping time. Thus, a capital cost savings ispossible by using only a single bed with the adsorption time ten timeslonger than the moving time plus the steam stripping time. The steamstripping time can be shortened by increasing the rate of steam flowduring regeneration. Alternatively one can use the tandem bed embodimentwhich can strip two or more sorbent beds using the same strippingchamber. This would further improve the capital cost savings byshortening the flow length of the each of the two beds. Operating with 2sorption beds each sorbent bed could have its thickness reduced by alarge factor, e.g., 10 times or more. Specifically, two or more thinsorbent material structures could be moved between an air captureposition and the stripping chamber. This would allow for the strippingof one bed, including cooling it back down to the ambient temperaturefrom the stripping temperature, while the other, regenerated, bed isfacing fresh airflow.

In the limit of thin contactors, the ceramic monolith could be replacedby a flexible thin sheet, or fabric, type of contactor, where the sheet,e.g., a fabric, is covered with the sorbent and is flexible, so onecould move it continuously on rollers rather than intermittently in anelevator. Such a flexible sheet could, in the limit, become a continuousprocess where the sorbent carrying sheet is continuously moved betweenthe adsorption and regeneration stages on a set of rollers, providedthat a seal could be effectively formed between the capture andstripping stages of the process. In the limit, as one shortens thelength, other embodiments become possible. For example, such otherembodiment might include a thin flexible contactor, for example formedfrom a thin sheet or a fabric. The flexible contactor can continuouslymove between the adsorption position and the regeneration position,e.g., on some continuous roller-type device. That would be theoreticallysimilar to the tandem version of the elevator embodiment described herein detail, in that white one part of the contactor as moving into theadsorption chamber, another part would be moving into the regenerationchamber. This essentially converts the batch elevator design to acontinuous moving process. This design depends upon reliable seals thatcan separate the adsorption chamber from the regeneration chamber whilethe flexible contactor is moving between the chambers.

The following computational model provides a useful procedure foroptimizing the efficiency of the CO₂ capture process and system of thepresent invention. This model is based upon the following Key ProcessPerformance Parameters

Key Process Performance Parameters:

-   -   Csh=Specific heat of the support skeleton material, in joules/kg        deg K.    -   d=Average pore size of skeleton    -   HRs=Heat of reaction of the sorbent(amine), in joules/mole of        CO₂    -   L=Loading, moles of CO₂/kg sorbent structure;    -   Ld/a=actual loading, in kg of CO₂ per square meter of monolith        air input area into the 230 cell Corning monolith    -   Ns=Density of CO₂ adsorption sites on the porous surfaces, in        number of sites per square meter of pore surface.

In general as one increases the loading one also wants high amineefficiency as defined by the fraction of amine sites present that areavailable to bind the CO₂. This is the reason for preferring primaryamines and also for adjusting the loading so as to minimize poreblockage. Experimental results indicate that the optimum loading thatbalances amine efficiency with increased loading is between 40-60% byvolume organic amine content relative to the porous substrate/skeletonto which it is attached or into whose pores it is deposited.

-   -   Pcm=Density of the skeleton material (e.g. silica or alumina),        in kg/cubic meter    -   PORc=Porosity,    -   PUR=Ratio of CO₂ released to trapped air, purity of CO₂    -   RH=heat of reaction; Ratio of sensible heat to heat of reaction        RH during regeneration SH/RH.    -   Save=Surface area per volume of the skeleton, in 1/meters        squared of surface/meters cubed    -   SH=sensible heat    -   TA=Time to fill to saturation with CO₂, time for adsorption,    -   TS=Time to regenerate using steam stripping,    -   w=skeleton pore wall thickness        Important design parameters to be considered in the design of        this process.

The porous structure is specified by the average pore/channel size d,and wall thickness of w. The porosity PORc is the ratio of the open wallarea to the total surface area perpendicular to the direction of airflow. In this model that is equal to the ratio of the average openchannel area to the total average area. For this approximation, thetortuous nature of the curves in the channels of the walls of the porousmedium is neglected. Thus, PORc=d²/(d+w)². The surface area per volumeis given by Savc=4 d/(d+w)²=4 PORc/d. The pressure drop is dependentupon the size of the openings in the channel, the void fraction of themonolith, length and velocity of air flow.

Sorbent Structure and General Operation of Sorbent

FIG. 12 is a schematic illustration of a cellular, ceramic substratestructure, of a type produced by Corning under the trademark CELCOR®,that can be used in a sorbent structure, in accordance with theprinciples of the present invention. The sorbent (e.g. an amine) iscarried by (e.g. coated or otherwise immobilized on) the inside of oneor more of the CELCOR®, cellular ceramic substrates, which provides ahigh surface area and low pressure drop, as CO₂ laden air flows throughthe substrate. The sorbent structure can comprise, e.g., a plurality ofthe CELCOR® cellular, ceramic substrates, stacked as bricks, or a singlesubstrate, having the type of pancake shape described above inconnection with FIG. 6 (i.e. front surface area much greater thanthickness), and the CO₂ laden air is directed through the cells of thesorbent structure. It is also contemplated that the sorbent structurecan be formed by et bedding the sorbent material in the, e.g., alumina,coating on the walls of the CELCOR® cellular, ceramic structure to forma monolithic sorbent structure.

It is also noted that an even more preferred structure is formed ofbricks of porous alumina, in place of the silica of cordierite. Althoughthe alumina structure is not physically and/or thermally as robust asthe silica structure, the less rigorous conditions met in this ambienttemperature capture process, and relatively low temperature strippingprocess, allow the use of the less robust structure.

In addition, it should be noted that the substrate, in addition to aceramic structure, an inorganic material, the sorbent structure can bean organic material such as is formed from a polymerized polyamine bycrosslinking the amine polymer to form a solid polymer. The solidpolymer should be capable of being extruded at low enough temperaturethat the polymer does not volatilize, nor be softened at the temperatureof the stripping steam, i.e., at up to 120° C., used for regeneration ofthe sorbent.

The binding sites in the porous structure are determined by the amountand dispersion of the amines throughout the porous structure. There arethree generally known classes of supported amine sorbents which havebeen used for the present situation. The presently preferred Class 1adsorbents are based on porous supports impregnated with monomeric orpolymeric amines (FIG. 12). The amine species are thus physically loadedonto or into the pores of the support structure. This class of sorbentsis described in the technical literature, for example in Xu, X. C., etal., Preparation and characterization of novel CO ₂ “molecular basket”adsorbents based on polymer-modified mesoporous molecular sieve MCM-41.Microporous Mesoporous Mat., 2003. 62(1-2): p. 29-45 and Xu, X. C., etal., Influence of moisture on CO ₂ separation from gas mixture by ananoporous adsorbent based on polyethylenimine-modified molecular sieveMCM-41. Ind. Eng. Chem. Res., 2005. 44 (21): p. 8113-8119 and Xu, X. C.,et al., Novel polyethylenimine-modified mesoporous molecular sieve ofMCM-41 type as high-capacity adsorbent for CO ₂ capture. Energy Fuels,2002. 16(6): p. 1463-1469. Class 2 adsorbents are based on amines thatare covalently linked to the solid support. Methods of forming suchClass 2 adsorbents in the porous structure of the present invention areknown to the art. This has most often been achieved by binding amines tothe ceramic monolith porous walls, e.g., silica oxides or aluminaoxides, via the use of silane chemistry, or via preparation of polymericsupports with amine-containing side chains.

Class 3 adsorbents are based on porous supports upon which aminopolymersare polymerized in-situ, starting from an amine-containing monomer. ThisClass 3 type was described for use as adsorbents for CO₂ capture byHicks, J. C., et al., Designing adsorbents for CO ₂ capture fromeffluent gas-hyperbranched aminosilicas capable, of capturing CO ₂reversibly. J. Am. Chem. Soc., 2008. 130(10): p. 2902-2903, and byDrese, J. H., et al., Synthesis-Structure-Property Relationships forHyperbranched Aminosilica CO ₂ Adsorbents. Adv. Funct. Mater., 2009.19(23): p. 3821-3832. Each of these adsorbent classes can be used forCO₂ capture and steam-regeneration studies.

A highly preferred sorbent structure is one in which the primary amineis incorporated into the monolith structure itself requiring only onestep to make it. Such a specific embodiment can be made fromplastic/polymers, which can survive because of the mild conditionsutilized in the system of the present invention. The monolith can be acomposite include inorganic non polymeric materials—such a compositewould have properties in terms of strength, porosity, stability thatcould be useful.

The following procedures can be followed to provide amine sorbentsupported on commercial particulate silica supplied by the PQCorporation (PQ-9023) or on mesocellular foam. For the preparation ofall the adsorbents, the silica substrate was first dried under vacuum at100° C. for 24 hrs. to remove absorbed water on the surface before use.A commercial particulate silica supplied by the PQ Corporation (PQ-9023)and a lab-synthesized mesocellular foam were used as supports. Thecommercial silica is characterized by a surface area of 303 m²/g, anaverage pore volume of 1.64 cc/g. and an average pore diameter of 60 nm.The mesocellular foam was prepared following a literature methodology,Wystrach, V. P., D. W. Kaiser, and F. C. Schaefer, PREPARATION OFETHYLENIMINE AND TRIETHYLENEMELAMINE. J. Am. Chem., Soc., 1955. 77(22):p. 5915-5918. Specifically, in a typical synthesis, 16 g of PluronicP123 EO-PO-EO triblock copolymer (Sigma-Aldrich) was used as templateagent and dissolved in 260 g DI-water with 47.1 g concentrated HCl. Then16 g of trimethylbenzene (TMB, 97%, Aldrich) was added at 40° C. andstirred for 2 hrs before 34.6 g tetraethyl orthosilicate (98%, Aldrich)was added to the solution. The solution was kept at 40° C. for 20 hrsbefore 184 mg NH₄F (in 20 mL water) was added. The mixture is later agedat 100° C. for another 24 hrs. The resulting silica was filtered, washedwith water, dried in oven, and calcined at 550° C. in air for 6 hr toremove the organic template before further use. The mesocellular foamsilica is characterized by a surface area of 615 m²/g, an average porevolume of 2.64 cc/g and average window and cell diameters of 12 nm and50 nm.

Generally, for a Class 1 sorbent, the amine compound may be applied tothe porous substrate structure by physical impregnation from the liquidor vapor phases. The amine compound can diffuse into the pores of thesubstrate structure. In this embodiment the pore volume becomes thecritical parameter determining loading and pores 5-15 nm beingpreferable but the conclusion of wanting as thin walls as possible andthus as high a porosity as possible that is also physically strongenough so that the monolith is structurally strong. As an example of thepreparation of the Class 1 adsorbent, 18 kg low molecule-weightpoly(ethylenimine) (PEI, MN˜600, Mw˜800, Aldrich) and 90 L methanol(99.8%, Aldrich) were mixed first for 1 hr. Subsequently, 30 kg ofamorphous particulate silica (PQ Corporation, PD-09023) [or a suitablesubstrate (175 in²) of the CELCOR® monolith] was added and the liquidstirred for an additional 12 hrs. The methanol solvent was later removedby rotavap, and the resulting supported adsorbent (“PQ-PEI”) was furtherdried under vacuum at 75° C. overnight before using.

For preparation of the Class 2 adsorbent, 90 L anhydrous toluene (99.5%,Aldrich) and 3 kg of particulate silica (PQ Corporation), or a suitablemonolith substrate (e.g., a brick of the CELCOR® monolith having a frontsurface area of 36 in², and a pore surface area of 175 in²) was mixed ina pressure vessel for 1 hr, then 30 kg of 3-aminopropyltrimethoxysilane(APTMS, Aldrich) was added into the mixture. The mixture was kept undervigorous stirring for 24 hrs at room temperature. The resultingsupported adsorbent (PQ-Mono) was recovered by filtration, washed withtoluene and acetone, and then dried overnight, under vacuum, at 75° C.

For the Class 3 adsorbent, particulate mesocellular silica foam (MCF)[[or a suitable substrate (175 in²) of the CELCOR® monolith]] is reactedwith aziridine (a highly reactive but toxic material) in a similarmanner as reported in the literature (Hicks, J. C., et al., Designingadsorbents for CO ₂ capture from effluent gas-hyperbranched aminosilicascapable, of capturing CO ₂ reversibly. J. Am. Chem. Soc., 2008. 130(10):p. 2902-2903). For this synthesis, 30 kg of MCF is dispersed in 90 Ltoluene in a suitable pressure vessel and the mixture is stirred for 1hr before adding 60 kg aziridine (which was synthesized in accordancewith the following procedure, Wystrach, V. P., D. W. Kaiser, and F. C.Schaefer, PREPARATION OF ETHYLENIMINE AND TRIETHYLENEMELAMINE. J. Am.Chem. Soc., 1955. 77(22): p. 5915-5918), immediately before use. Aftercontinuous stirring for 24 hr, the resulting supported adsorbent(MCF-HAS) is filtered, washed with toluene and ethanol, and driedovernight under vacuum at 75° C.

CO₂ laden air is passed through the sorbent structure, which ispreferably pancake shaped, i.e., the dimension in the direction of theair flow is as much as two orders of magnitude smaller than the othertwo dimensions defining the surfaces facing in the path of the air flow,and the amine sites on the sorbent structure binds the CO₂ until thesorbent structure reaches a specified saturation level, or the CO₂ levelat the exit of the sorbent structure reaches a specified value denotingthat CO₂ breakthrough has started (CO₂ breakthrough means that thesorbent structure is saturated enough with CO₂ that a significant amountof additional CO₂ is not being captured by the sorbent structure).

When it is desired to remove and collect CO₂ from the sorbent structure(and to regenerate the sorbent structure), in a manner described furtherbelow in connection with FIGS. 10a-h , the sorbent structure is removedfrom the carbon dioxide laden air stream and isolated from the airstream and from other sources of air ingress. Steam is then passedthrough the sorbent structure. The steam will initially condense andtransfer its latent heat of condensation to the sorbent structure, as itpasses from and through the front part of the sorbent structure untilthe entire sorbent structure will reach saturation temperature,thereafter as the steam contacts the heated sorbent it will furthercondense so that for each approximately two (2) moles of steam willcondense to liberate sufficient latent heat to provide the heat ofreaction needed to liberate one (1) mole of the CO₂ from the primaryamine sorbent. As the condensate and then the steam pass through andheat the sorbent structure, the CO₂ that was previously captured by thesorbent structure will be liberated from the sorbent structure,producing more condensed water in providing the needed heat of reactionto liberate the CO₂ from the sorbent structure and be pushed out of thesorbent structure by the steam or extracted by an exhaust fan/pump. Thistechnique is referred to as “steam stripping” and is also describedfurther below. The steam is passed through the sorbent structure tocause the release of the CO₂ from the sorbent; for energy efficiencycost reasons one would want to minimize the amount of steam used andthat is mixed in with the CO₂ effluent. Thus, whatever is (or can be)condensed, upon exiting the regeneration chamber, the condensate can beadded to that generated in the regeneration chamber, and recycled to beheated and converted back into steam for further use.

The stripping process usually will be terminated at the onset of steambreakthrough, when the amount of uncondensed steam emerging from thebackend of the sorbent structure becomes large compared to the newlyliberated CO₂. The exact conditions for terminating the injection of newsteam will be determined by balancing the increased fraction of CO₂removed with the increased cost of energy as the steam process becomesless efficient in terms of the ratio of CO₂ liberated per energy ofsteam used. That energy needs to be replaced when the steam andcondensate are reheated for the next stripping cycle. The exactspecification will vary with the effectiveness of heat recovery and thecost of the process heat used in a particular application.

The System In designing the structure of the system incorporating thepresent invention to be commercialized, the following design parametersshould be considered. If Ns is the number of CO₂ binding sites persquare meter of pore surface, Av is Avogadro's number, and if thedensity of the material of the skeletal structure is Pcm, the porousskeleton will have a density Pc given by Pc=(1−PORc)Pcm; then theloading L in moles per kilogram of sorbent structure is given byL=NsSavc/AvPc=4NsPORc/AvdPcm(1−PORc)If one solves the above expression for PORc, one findsL=(4Ns/AvPcm)(1/(2w+w2/d))

Since it is desirable to maximize the loading of CO₂ adsorbed by thestructure, the polyamine sorbents provide the desired high Ns. In anycase the above analysis makes clear that it is preferred to have as thinwalls as possible, between the pores/channels in the porous support. Theloading in moles/kg is to first order, independent of the size of thepores, with the decrease in Savc, as the porosity is increased by makingthe pore size larger, cancelled to first order by the decrease in thedensity of the porous support, Pcm.

One can insert the values for Av and for Pcm of 2,500 Kg/m3 (note:averaging the difference in the values for quartz and fused silica) andconvert Ns to Nsn which is the number of attachment sites per squarenanometer, where w and d are in nanometers, to find: L=1.33(Nsn/w(1+w/2d) moles/kg, of the skeleton structure. For Nsn=5 sites per squarenanometer and w=2 nanometers and d=5 nanometers, a porosity of about 0.5results in a surface area per gram of 400 mm² and L=2.5 moles/kg. of theskeleton structure.

The actual loading capacity of CO₂, as kg/m3 of air input, Ld/a, wherethe thickness of the support wall is Wc and the length (in the directionof airflow) of the monolith is Lm is given byLd/a=L(0.044)(Pcm(1−PORc))Savm Wc Lm, which substituting for L,

-   -   Ld/a=(Ns Savc/Av Pcm(1−PORc))(0.044)(Pcm(1−PORc))Savm Wc Lm;    -   Ld/a=Ns(0.044)/Av)(Savc Savm Wc Lm), Substituting for Savc,    -   Ld/a=Ns(0.044)/Av)(Savm Wc Lm)(4/d(1+w/d)²).

In one example, using the Corning 230 cell CELCOR monolith, the poreflow length Lm is 0.146 meter, the surface area per volume of themonolith Savm is about 2000 m2/m3 and the pore wall thickness of themonolith Wm is 0.265 mm, determined from Ld/a=L(0.044 kg/mole) (Pc Savm0.146 Wm), for an amount of CO₂ in kg/m2 area of air input. A generaldesign criteria is to make L and Ld/a as large as possible, constrainedby the pressure drop constraint, i.e., limited by the force of the windand/or fan array, which is met in the first embodiment of the presentinvention using modeling results for the Savm of the 230 cell Corningmonolith, and the pore length, in the direction of air flow, of 0.146 mand input air flow velocity of 2.5 m/sec.

The walls of the monolith should have the desired PORc, and number ofattachment sites to provide a high Nsn. Wm is determined based uponoptimizing (minimizing) the pressure drop/Savm, which in turn will beconstrained by a limit of how small one can make Wm to have acceptableloading, based upon other constraints (see below). It should be notedthat L increases as w decreases, and d increases, but Ld/a decreases,with increasing pore size for a fixed w, because as the porosityincreases Pc decreases. In general terms, the optimal design has thesmallest w possible, and a porosity that balances the impact of the poresize on the performance parameters described below. It must beremembered that the amine compound may be impregnated as a liquid in thepores of the monolith as well as, or in lieu of, being supported on thewalls of the pore structure.

Air capture following the present invention, is a relatively mildcondition. This feature of the present invention allows the use of amuch less robust structure for the monolith. In particular this permitsthe use of relatively thin walls made out of material with high porosityon to which sorbent is deposited; one such material is alumina. Thiswill save in cost, using materials that are generally less robust andtherefore less costly to manufacture.

Performance Parameters.

Ratio of SH/RH. As indicated above, for the present invention, the ratioof sensible heat of the sorbent support structure (SH) to heat ofreaction of the sorbent (HRs) that is lost, during regeneration, is akey performance factor (a main reason for needing high loading in thiscase). It depends on the loading L, namely SH/HR=Csh·ΔT/L·HR·s·WC, whereCsh is the specific heat of the substrate in joules per kg per degreeKelvin, HRs is the heat of reaction of adsorption, per mol of CO₂, injoules per mole of CO₂, and WC is the working capacity of the bed in theprocess used (e.g. the fraction of the loading that is captured eachcycle).

Assuming (conservatively) a Csh of about 1 kj/kg degree K. For the solidsubstrate, a ΔT of 80° C., and HRs=84 kj/mole (about 35 KT), for aprimary amine, and WC=1/2, SH/HR=1.9/L. The process needs the high HRsof the primary amine to achieve good loading of the Ns sites, at ambient25° C. temperature, and for the low partial pressure of CO₂ in air. Byusing primary amines only, the fraction of sites that bind CO₂ wouldincrease at ambient temperatures and ambient concentrations of CO₂, andbe very comparable to the results for the high concentrations of CO₂ inhigh temperature effluent gas (45-65 C). It was this surprising resultthat makes it possible to use primary amines for effective air captureof CO₂. The prior art believed that successful air capture required theuse of the much more strongly binding/uglier heat of reaction (2-4 timesthat of primary amines) sodium hydroxide, as the sorbent. This approachwas much less economical, as much higher temperatures were required toregenerate the sodium hydroxide, resulting in the need for higheramounts of costly energy.

The general design criteria for the present invention is for SH/HR to beas small as possible and for the recovery of SH to be as high aspossible. But in any event, SH/FIR should be less than or equal to one,and most preferably between ½ and 1. It is important to note that thisrequirement only depends upon the specific loading, in moles/kg of thestructure, and thus again to first order, only depends upon increasingNsn/w, for the case of surface attachment. However, there is a secondorder dependence that decreases the SH/RH ratio as the pore size isdecreased.

TA—The Adsorption Time—The time to complete adsorption, TA, has beenmodeled for the six inch thick (in direction of air flow) 230cells/cubic inch Corning CELCOR monolith. Using those results one candetermine TA from the following relationship, where the left side is theamount of CO₂ that enters the device and is captured, and the right handside is the fraction of the input CO₂ that is both captured by the amineand collected during steam stripping: P CO₂ Vin FC TA=La/d FS WC, where

-   -   P CO₂ is the density of CO₂ in air=7.6×10⁻⁴ kg/m3,    -   Vin is the velocity of the input air, FC=fraction captured,    -   FS=fraction of bed saturation that is achieved, and    -   WC=fraction of CO₂ captured that is collected.        Thus, TA=La/d FS WC/P CO₂·Vin FC=Ns(0.044)/Av)(Savm Wc        Lm)(4/d(1+w/d)²)FS·WC/P CO₂, Vin FC

At very low temperature locations, it may be possible to use secondaryamines as well, and in filet one can tune the system of the presentinvention by varying the ratio of primary and secondary amines, in orderto limit the heat output. Generally, increasing WC or L, increases theenergy efficiency of the process, and reduces the costs of providingexternal heating.

Thus, as mentioned earlier, SH/HR varies as 1/w(1+w/2 d), and theadsorption time TA varies as 1/d(1+w/d)², so that both improve as w getssmaller; but as d gets smaller, SH/HR falls but TA improves, i.e., isreduced. For estimating TA, use the same values as used for estimatingL, i.e., 2 nm for w and 5 nm for d, which gives a porosity of 0.5 forthe skeleton structure. In the case of physical impregnation, higherporosities are desirable, only constrained by the need for structuralstability of the monolith.

PUR—The Purity of the Collected CO₂—As a final performance factor, thepurity of the CO₂ that is collected is significant in those situationswhere the stripped CO₂ is intended to be compressed for pipelineshipment, to be used for either enhanced oil recovery or forsequestration. The primary concern is about trapped air and not watervapor, which is easily removed in the initial stages of compression ifthe CO₂ is to be pipelined. For other uses where the carbon dioxide isnot compressed significantly, such as a feed for algae or input to otherprocesses, the presence of air is often not an issue. The purity of theCO₂ is primarily affected by the amount of air trapped in the capturesystem when it is subjected to the steam stripping. Therefore, thisrequires providing for the removal of such trapped air before commencingthe stripping of the CO₂, e.g., introducing the stripping steam.Removing any trapped air is also desirable as the oxygen in the air cancause deactivation of the sorbent when the system is heated to thestripping temperature, especially in the presence of steam.

Oxygen can be readily removed by pumping out the air from the supportstructure, to form at least a partial vacuum, before it is heated to thestripping temperature. As an unexpected advantage, when using primaryamine groups as the sorbent, reducing the pressure in the structure willnot immediately result in the correlative toss of any sorbed CO₂, whenthe sorbent is at the relatively most ambient temperatures, when thepartial pressure is reduced by pumping. The CO₂ is not spontaneouslyreleased from the amine at such low temperatures. Such release, as hasbeen shown experimentally, requires a stripping temperature of at least90° C.

This process can be carried out where the initial capture phase resultsin substantial saturation of the CO₂ on the sorbent, or until it resultsin only, e.g., about 60-80% of saturation by the CO₂. This willsubstantially reduce the capture cycling time to an extentproportionally as much as 40%, so that the ongoing cycling of theprocess results in a greater extraction of CO₂ per unit time. Generallysorption slows as the sorbent closely approaches saturation.

Details of preferred embodiments of this invention are given in thecontext of the following specific examples of CO₂ capture and strippingsystems, with reference to the attached drawings.

FIGS. 17a, b and 18 a, b are schematic illustrations of several waysthat carbon dioxide can be removed from an atmosphere, according to theprinciples of the present invention.

When a sorbent structure, such as a substrate carrying a primary aminesorbent, is in the CO₂ capture position (e.g. the position of substrate600, in FIG. 6, or in FIGS. 17a and 18a ), carbon dioxide laden air isdirected at the substrate (e.g. by a single large fan 604, shown indashed lines, in FIG. 6, or by a plurality of smaller fans 2004, asshown in FIGS. 22-23), so that as the air flows through the substrateand into contact with the sorbent, the carbon dioxide contacts thesorption medium on the surfaces of the substrate, and is substantiallyremoved from the air. Thus, carbon dioxide laden air is directed at andthrough the substrate so that carbon dioxide in the air comes intocontact with the medium, carbon dioxide is substantially removed fromthe air by the medium, and the CO₂-lean or leaner air from which thecarbon dioxide has been substantially removed, is directed away from thesubstrate, back into the atmosphere.

In the embodiments of the above figures, the substrates are movedbetween the CO₂ capturing zone and the CO₂ stripping/regenerationchamber 2006. When a substrate is moved to the CO₂ stripping chamber2006, i.e., the lower position as shown in FIGS. 6, 17 b and 18 h, thesubstrate is at substantially ambient temperature, the heat of reactionof the sorption activity having been removed by the convective effect ofthe blown mass or air from which the CO₂ was removed, which is fargreater than the amount of CO₂.

-   -   Any trapped air in the substrate 2002 and chamber 2006 can be        pumped out, e.g., by an air evacuation pump 2023, or even by an        exhaust fan, to form a partial vacuum in the chamber 2006. Next,        process heat, e.g., in the form of saturated steam from the        Steam co-generator 2019, is directed at and through the        CO₂-laden substrate 602, 2002 in the stripping chamber 2006.

Carbon dioxide is removed from the sorbent (stripped oft) by the flow ofrelatively hot superheated steam; the incoming steam is at a temperatureof not greater than 130° C., and preferably not greater than 120° C.,and most preferably not greater than 110° C. The vapor, comprisingprimarily carbon dioxide and some saturated steam, flows out of thestripping chamber 2006, through exhaust conduit 2008 into a separator,where any steam present is condensed. The liquid condensed water isseparated from the gaseous stripped CO₂. Some of the steam that iscondensed in the sorbent structure itself during the stripping processeither will be collected in a drain at the bottom of the regenerationchamber (e.g., by tipping the structure slightly off level) or will beevaporated upon pumping out, and reducing the pressure in, theregeneration chamber following the completion of the steam strippingprocess. That evaporation of the condensed steam will cool down thesorbent structure before it is put back in contact with the air tocapture more CO₂ (this also will mitigate the tendency of oxygen todeactivate the sorbent by oxidizing it). Some of the water left in theporous structure can also be removed by the effect of passing the airthrough the device in the adsorption step (this will depend upon theambient humidity). It has been shown experimentally, however, that theeffectiveness of capture increases in the presence of moisture. This iswell known to the art and results from the fact that dry sorbent mustuse two amine sites to bind CO₂ to the sorbent when dry, 50% amineefficiency, to only one amine binding site per CO₂ captured in thepresence of high humidity, 100% potential amine efficiency. Thepotential amine efficiency may still be limited by pore blockage and thepractical decision of how much of the bed is to be saturated with CO₂before one terminates the adsorption process and moves the sorbentstructure to the regeneration step.

The stripped CO₂ from the regenerated sorbent is in turn pumped into astorage reservoir where it is maintained at slightly elevated pressurefor immediate use, e.g., to provide CO₂-rich atmosphere to enhance algaegrowth, or the carbon dioxide gas can be compressed to higher pressures,by means of compressor 2014, for long term storage or to be pipelined toa distant final use, e.g., sequestration or treating of oil wells ornatural gas wells to improve production. During any initial compressionphase, the CO₂ is further purified by the condensation of any remainingsteam, which water condensate is in turn removed, by known means.

The substrates 602, 2002, are alternatively moved between, e.g., upperand lower positions, by means of an elevator system of, e.g., pulleys orhydraulic lifts. It is recognized that the faster the cycling time thelower the overall cost to obtain an annual production of captured CO₂.It has been found that the time required for the stripping step,including the moving of the bed, the initial pumping out of the air, thesteam stripping time, and the cooling period, and the time to move backto the adsorption stage, can be several times less than the time of theCO₂ capture step enabling a one bed embodiment with a high percentage ofthe time (90%) the bed in the adsorption mode. Alternatively one can goto very short times limited by the moving plus steam stripping time andthen use the embodiment where two or more sorbent structures arestripped in one stripping chamber, successively.

When commercially siting these CO₂-extraction facilities, it isanticipated that one option includes their being scaled to a capacity toremove on the order of One Million (1,000,000) metric Tonnes of CO₂ peryear from the atmosphere. Such a facility will utilize at leastapproximately 500 such reciprocally moving substrate modules, where eachmodule will have major rectangular surfaces extending perpendicular tothe flow of air with an area of as much as about 50 square meters, and athickness, in the direction of flow, of most preferably not greater thanabout six (6) inches, but usually less, e.g., as low as 0.06 ins (1.5mm). Each monolith module is preferably formed from brick-shapedmonolith elements, each the desired thickness of the module, but havinga face surface of about 6 ins. by 6 ins., so that each module may beformed of about 2000 such bricks, stacked together.

These arrays of modules are preferably arranged in the chevron patternshown in FIGS. 21a,b , where the point of the chevron preferably facestowards the prevailing wind and the modules are arranged along the armsof the chevron so that they are all exposed to the prevailing wind,and/or to their fans, or other means of providing a flow of airdescribed herein. The spacing between the chevron rows is determined bythe rate at which the low CO₂ air ejected from the first row iseffectively mixed with the ambient air so that the air entering thesecond row will be close to the concentration of the ambient air. Ingeneral, calculations suggest that this will be on the order of 100meters. However, certain conditions could reduce the distance, forexample, elevating the adsorption chamber off of the ground, or thepresence of prevailing winds or unusually beneficial terrain will allincrease mixing, and thus shorten the necessary separation distance.

In the blended approach, in which small percentages by volume ofeffluent gas are mixed into the air, one embodiment could be to have thefirst row be ambient air only and then taking the depleted air andmixing the effluent gas into the depleted air for input to the secondrow. For Cases Where One Has Only A Limited Amount Of Effluent gas ToMix Into The Air And Where it is Desired To Remove Considerably MoreTotal CO₂ than is being emitted in the effluent gas, one can adjust therelative amounts of air and flue mixing, by both adjusting thepercentage of flue mixed in with the air and/or by dividing the unitsand varying mixtures of flue and air streams in different units,including some that are pure air capture. Thus using the air/flueblender, one can generally adjust fraction of the total amount of CO₂collected that is above that emitted in the flue to any level desired.

The sorbent medium preferably has primarily primary amine groups as theactive capture sites for CO₂ but may include some secondary aminegroups. Examples of such suitable adsorbing compounds which aresupportable on the structures of this invention includepolyethyleneimines, hyperbranched aminopolymers andpropylethylenediamine, all as discussed above under Classes 1, 2 and 3.

As a means to further improve the efficiency of the method and system ofthe present invention, it can be useful to add a small proportion ofeffluent gas, from a hydrocarbon-fueled energy source used for theprimary process adjacent the CO₂ capturing plant, as shown in FIGS. 17aand 19. As schematically shown in the figures herewith, effluent gasfrom the primary process is initially passed through a pre-treatmentstage 2032 and treated to remove any solid or liquid impurities and anygaseous materials that may interfere with the effectiveness of thesorbents, such as sulfur-oxygen compounds. Preferably not more than 5%by volume of the treated effluent gas is then blended in a gas blender2004 to be mixed with the incoming Ambient Air, before it is passed tothe sorbent structure 2003 for CO₂ capture. The amount of effluent gasadded is more preferably not more than 3% by volume and most preferablynot more than 2% by volume. The small amount of the treated effluent gasadded should not have a significant effect on the temperature of theincoming air flow to the sorbent structure 2003, but should result in arelatively substantial increase in CO₂ concentration in the incomingair, thus rendering the capture of the CO₂₂ more efficient. Usingtheoretical calculations, it can be shown that increasing the effectiveCO₂ concentration of the mixture by the addition of effluent gas in theproportion of 3%, increases the concentration of CO₂ in the air by afactor of five to ten times; however, it remains over 30 times less CO₂concentration than the effluent gas. However, above that concentrationfrom the small addition of effluent gas, the temperature rise from thesorption heat of reaction becomes significant, reducing the efficiencyof CO₂ capture from ambient air, such that designs for effluent gas needto be utilized. Thus, limiting the amount of effluent gas added is a wayto avoid the cost associated with providing the cooling needed toprevent overheating.

It should be noted that the preferred siting for such a CO₂-extractionfacility, in addition to being adjacent a source of suitable processheat, should be in an area having regular wind flow patterns. In thismanner, if there are strong winds available, natural wind flows can beused to drive the air through the substrate, without requiringadditional power to drive the fans. As a result of naturally occurringwinds, the energy of the fans can be at least partially replaced, byprevailing winds, or by a solar driven source (which can, e.g., providethermally-driven air currents), which will further improve theenergy-efficiency and cost reduction of extraction of carbon dioxidefrom atmospheric air.

Moreover, as an alternative to moving the substrates carrying sorbentbetween capture and regeneration (stripping) chamber locations, byproviding suitable valve and piping arrangements, with proper sensorsand control elements, the sorbent structure modules can remainsubstantially in one location and the flows to and through and away fromthe sorbent can be controlled, as is schematically shown in FIG. 19,herein. In the automated system of FIG. 19, means for generating the airflows, the flow of process heat, and the flow of carbon dioxide awayfrom the substrate, can be switched using valves, as carbon dioxide iscaptured from the air and then extracted from the medium, as will bereadily apparent to those in the art.

The substrates 2002 and 3001 (in FIGS. 17-18 and 22-24, herewith) areporous, so that air directed at a substrate can flow through thesubstrate. When a substrate is in an air extraction position (e.g. theposition of substrate 2002, in FIG. 17A), carbon dioxide laden air isdirected at the substrate (e.g. by a fan 704 shown in dashed lines), sothat as the air flows through the substrate, the carbon dioxide contactsthe medium and is substantially removed from the air. Thus, carbondioxide laden air is directed at and through the substrate so thatcarbon dioxide comes into contact with the medium, carbon dioxide issubstantially removed from the air by the medium, and air from which thecarbon dioxide has been substantially removed is directed away from thesubstrate. When a substrate is moved to the carbon extraction position(e.g. the position of the substrate labeled 2006), process heat, in theform of saturated steam, is directed at the substrate (e.g. 2005, inFIG. 17B), and carbon dioxide is removed, together with any remainingsteam (the direction shown by arrow 708, in FIG. 7) by a source ofsuction located in conduit 710 (FIG. 7) and in, or adjacent to,Separator 2009 (in FIG. 17A), by which carbon dioxide that has beenremoved from the medium is drawn away from the substrate.

Rather than moving the substrates between two physical locations, theconduits for generating the air flows, the flow of process heat, and theflow of carbon dioxide, to and away from the substrate can be switched,as carbon dioxide is captured from the air and then extracted from themedium, as will be readily apparent to those in the art.

It should also be noted that in all of the versions of the inventiondescribed above, the removal of carbon dioxide from the air can becarried out so that the CO₂-extraction stage does not fully saturate theamine groups, i.e., the sorption medium does not reach equilibriumconditions. This results in a shorter cycle time, and because of theslower adsorption rate occurring as the amine approaches its equilibriumsaturation point, over an extended period of operation of the process,using the shorter cycle times may result in greater effectiveCO₂-extraction from the atmosphere.

Vertical Elevator Concept of FIGS. 10a and 10h and 22f , 23 a,b and 24a-c

These figures show schematic illustrations of the elevator and chamberstructures, designs that further enhance the system with which carbondioxide can be captured from CO₂ laden air and then stripped usingprocess heat steam, according to the principles of the presentinvention. Furthermore, by operating the elevator vertically, when theregeneration stage is the lower portion, the weight of the array, whichis supported from the upper surface, makes the box self sealing.

Specifically, in these drawings, a rectangular carbon dioxide capturestructure 1000, 3000 is illustrated, which has a sorbent structure 3001,as described herein, that can be moved between a position where it isbrought into contact with CO₂ laden air, to capture carbon dioxide fromthe air. The rectangular sorbent structure 3001 has a relatively largearea perpendicular to the air flow compared to its thickness, and isoriented vertically in relation to a substantially horizontal flow ofCO₂ laden air. The carbon dioxide sorbent capture structure 3001comprises a solid, nonporous top member 1002, 3002, that is preferably asolid metal plate; the sorbent structure 3001 being supported betweenthe top and bottom members 3002, 3003. The bottom member is also asolid, plate 3003, that is preferably a solid metal plate, as it assistsin the pushing out of air from the stripping/regeneration chamber. Whenlocated in a stream of CO₂ laden air, the sorbent structure 3001 isexposed to the CO₂-laden air stream which passes through its large areafaces, directed by an array of exhaust fans 3010, or by a prevailingwind; the sorbent captures the carbon dioxide from the air flowingthrough the sorbent structure. The highly porous sorbent structure 3001,1004 provides a high surface area and low pressure drop.

When the sorbent has captured the desired amount of carbon dioxide fromthe air, the air flow can, if desired, be closed off. While the air isflowing through the sorbent, the effluent air from the sorbent structure3001, is substantially depleted of carbon dioxide (preferably about 95%depleted of carbon dioxide). It is understood that under certainsituations the relative vertical positions of the capture and strippingchambers can be reversed, though it is generally preferable having thecapture unit on top, because of greater mixing higher off of the ground.

In the regeneration position, the sorbent structure 3001 is then heatedby a flow of process heat (preferably from a co-generation system andprocess, as described further herein). As described above, the processheat is preferably converted via a heat exchanger to saturated steam,which is admitted into the lower sealed chamber after the air isexhausted, to strip the CO₂ from the sorbent, as described above, by thecombined effect of the heat and the steam. As the regeneration box 1014is heated (preferably by the “steam stripping process described herein),the carbon dioxide is separated from the sorbent structure, and is drawnoff together with any uncondensed steam, to a separation chamber, whereany remaining liquid water is removed, permitting more steam tocondense, as it cools. The purified carbon dioxide can then be used orpressurized and sequestered, as desired. After the carbon dioxide isstripped from the sorbent structure 3001, and withdrawn from the sealedchamber, the thus regenerated sorbent structure is moved upwardly backto the CO₂-capture position, as shown by the series of drawings of FIGS.23a-c , and schematically in FIGS. 17A-B and 18A-B.

FIG. 10b -1, 2 schematically illustrates an alternative to the structureand technique of FIG. 10a . The pair of carbon dioxide capturestructures 1000 can alternatively move between the upper and lowerpositions, so that the carbon dioxide capture structure in the upperposition is removing carbon dioxide from the carbon dioxide laden airand carbon dioxide is being removed from the sorbent structure that isin the lower regeneration or stripping position. The two sorbentstructures also can act as counterweights for each other as they move upand down.

Steam Stripping

-   -   a. There are two techniques that are contemplated for the steam        stripping process. The preferred technique is referred to as        “steam stripping with steam only”.    -   b. It should be noted that an additional step of evaporative        cooling of the sorbent bed before raising it back to the        adsorption position will reduce the risk of degradation when the        oxygen in the air would contact the sorbent at an elevated        temperature. This is achieved by using a sufficiently strong        exhaust pump from the stripping chamber so that at least some of        the condensed steam is vaporized, at the lower resulting        pressure, thus removing its latent heat with the resulting        cooling of the sorbent monolith.

Steam stripping, as described above, would be performed in the foregoingmanner in connection with FIGS. 17-23, herewith.

Sorbent Characteristics

In general, the sorbent that forms the sorbent structure ischaracterized by its ability to adsorb (capture) CO₂ at low (ambient)temperature and concentration and regenerate at higher temperature (ofprocess heat steam) and high concentration (because CO₂ that is capturedby the sorbent structure would have a high CO₂ concentration as thestripping occurs). The concentration of CO₂ in CO₂-laden air is on theorder of 300 times smaller than the concentration of CO₂ in effluentgases (a major contributor to the presence of CO₂ in the atmosphere).The CO₂ can be captured from a stream of CO₂ laden air at ambienttemperature (e.g. about 20 degrees C. in many climates); and thetemperature of the steam used in the steam stripping process describedabove is at a temperature of about 100-120 degrees C., based on theLangmuir isotherm or Langmuir adsorption equation (which is known tothose in the art). The temperature of the sorbent structure during aircapture should not be too high, but preferably should remain at thelower ambient temperature when the CO₂ is captured. Otherwise, the CO₂loading capable of being achieved by the sorbent will be reduced by theincreased temperature as, for example, described in the well-knownLangmuir Isotherm Equation. Thus, while the sorbent material ispreferably an amine, the specific amine material or other suitablesorbent may vary for different climates to optimize the net CO₂ that iscollected during each cycle of capture and regeneration in which thesystem and process of the present invention will be used.

Co-Generation and Process Heat

As explained above, according to the present invention, process heat isused to provide the steam that is used in the “steam stripping” processand system described herein, to remove CO₂ from the sorbent structureand regenerate the sorbent structure. It is also preferred that theprocess heat is provided by a co-generation process and system, where aprimary process (e.g. a petrochemical plant, a utility facility, etc.)produces steam that is provided directly to the system of the presentinvention and used to remove the CO₂ from the sorbent structure andregenerate the sorbent structure.

Industrial plants such as power stations and petrochemical plantsgenerate large amounts of steam. The higher the pressure at which thesteam is generated the higher the thermal efficiency that can beachieved and the use of co-generation systems (where gas turbinesgenerate electricity and the hot gases from the turbine are used togenerate more steam) also improves the overall thermal efficiency of aCO₂ capture system and process, according to the principles of thepresent invention.

There are many different designs of steam systems within thepetrochemical industry due to the different mix of electric and turbinedrivers for pumps and compressors, the temperature required for columnreboilers and preheating duties, etc. These affect both the amount ofsteam generated and also the number of pressure levels at which thesteam is supplied to the process. Given these qualifications a “typical”petrochemical steam system design includes steam that is generated atvery high pressure (VHP) by the large boilers and co-generationfacilities. This VHP steam is passed to and through turbines which areused to drive motors or compressors and result in exhaust steam at lowerpressures. The next levels of steam are HP and MP which are providedfrom the extraction turbines or by direct let-down from the VHP steammain. The final steam level is LP and is provided by the exit steam fromthe turbines and by direct let-down. Each steam level provides steam todifferent users and any excess steam is passed down to the next steamlevel. Thus the LP steam receives all the steam that cannot be usedusefully at the higher steam levels. It is important to recognize thatin a petrochemical facility the steam system must be flexible asdifferent sections of the process may be off-line or starting-up,shutting down or be at lower than design rates at different times. Thisis different from a utility power plant where the steam only has toprovide one function generating electricity.

The value of steam depends upon the pressure level. The base cost of theVHP steam is fixed by the capital and operating costs of generation.Therefore, as the steam is reduced in pressure after passing through andpowering the turbines, it becomes less effective for generatingadditional electricity, and the value of the steam is reduced.

In the case of the proposed use of the superheated steam, at ambientpressure, to release the CO₂ from the sorbent structure, the followingadvantages appear to exist for a typical large petrochemical facility:

-   -   a. At a proposed steam level for the present invention (2-10        psig) the cost of the required steam will be very low for a        typical facility, although this will vary between facilities        depending upon the amount of LP steam that is available.    -   b. In comparison with a conventional amine system in an effluent        gas capture system, that requires stripping steam at        approximately 60 psig, the cost of steam used in the present        invention is significantly lower. In addition it is much more        likely that there will not be an adequate supply of 60 psig        available and that additional VHP steam would have to be        generated. This would raise the cost of the 60 psig steam as it        would either have to be charged at the full cost of VHP steam or        additional turbines would have to be installed to recover power,        but this would involve significant capital costs.

In most power plants a steam supply is ex acted from the low pressureturbine to heat the feed water to the system. This extracted steam wouldbe suitable for use in the proposed process of this invention to removeCO₂ from the sorbent structure, as it is provided in the co-generationof electricity and industrial heat. In the cogeneration of electricityand CO₂, as described in this embodiment of the present invention, it ispossible to use very low pressure (2 lb above atmosphere pressure andtemperature around 105° C.) and can return the condensate to heat theboiler since the process heat being used is only the latent heat of thesteam, so that substantially 100° C. condensate is returned to theboiler. While cogeneration of electricity and industrial heat reducesthe electricity produced, it does raise the overall thermal efficiencyof using the heat generated to useful energy from 35-40% to 85-95%. Itis thus favored when there are nearby uses for the low temperature andpressure steam (usually 120 deg C., 2 lbs above atmosphere steam). Inthe cogeneration of electricity and CO₂ capture, one can site thefacility close enough to use the low temperature and pressure steam; andby being able to use even lower pressure and temperature steam andrecirculating the hot condensate in the process heat steam loop back toheat the boiler, one can minimize the impact on electricity generationand thus the cost of the steam.

Additional Comment Regarding Mixing of Ambient Air and Effluent Gas

In addition to the capability of the present invention to capture carbondioxide from ambient air alone, without capturing carbon dioxide fromeffluent gases, the principles of the present invention can be appliedin a new and useful way to enhance and make more efficient the removalof CO₂ from a combination of CO₂ laden air and effluent gas (e.g. from afossil fuel plant). A relatively large volume ratio (e.g. 97-99%) of CO₂laden air is mixed with a relatively small volume of effluent gases(preferably not more than about 3% effluent gas, and more preferably notmore than 2% effluent gas). Effluent gas contains a relatively highconcentration of CO₂; therefore, to produce a fluid stream in which theCO₂ in the effluent gas adds sufficient CO₂ to the air to make the costof removal of CO₂ from the combined gases more advantageous, and alsoprovides benefits in that the CO₂ laden air cook the effluent gases.Application of the principles of the invention to produce such a mixedgas stream is believed to make the process of the present inventiondescribed above particularly efficient. The CO₂ in the relatively largevolume of mixed CO₂ laden air is still relatively low concentration CO₂,in accordance with a basic concept of this invention's paradigm; thesmall volume amount of effluent gas increase the concentration of CO₂ inthe fluid stream, and makes the applicant's process even more costefficient in the manner in which it removes CO₂ from an ambient fluidstream. At the same time, the high volume of ambient air cools theeffluent gases so that the combined gases enable the sorbent temperatureto remain in a temperature range in which the process of this inventionis most efficient when using the amine as the sorbent.

Examples of useful methods of admixing the effluent gas with the air isshown in FIGS. 25 and 26. In FIG. 25, a jet of effluent gas 3031 isinjected into a flow of ambient air, to form a mixture before passing tothe array of fans as shown in FIG. 22. In FIG. 26, a particular designis presented where effluent gas is injected through a centrally locatedpipe 3035 into an air stream passing from a concentric ring header,which defines multiple orifices, located circumferentially around thecentral effluent gas inlet. Again, the mixture is passed through thefans for additional mixing before entering the sorbent. In this case, ofcourse, the fans are not acting as exhaust fans drawing the air throughthe sorbent structure.

In Summary

Accordingly, with the structure and technique of FIGS. 10a-10h , andFIGS. 17-23, carbon dioxide laden air is directed through the verticallyoriented carbon dioxide capture structure 1000, 2002 that has sorbentcapable of adsorbing, or binding, carbon dioxide, to remove carbondioxide from the air. When carbon capture is completed, the verticallyoriented carbon dioxide capture structure is lowered into a regenerationenclosure 1014, 2006, where process heat is directed at the carbondioxide capture structure, to separate carbon dioxide from the sorbent,and regenerate the sorbent. The carbon dioxide capture structure 1000,2002 is selectively raised out of the regeneration enclosure to aposition that, after the structure cools down to near ambient, is in theflow carbon dioxide laden air, so that the regenerated sorbent cancontinue to be used to adsorb or capture carbon dioxide, from the flowof carbon dioxide laden air. In addition, the present invention can becarried out using the structure and technique of FIGS. 11a, 11b , wherea flow of sorbent-carrying porous particles is selectively fed into acarbon dioxide removal chamber 1104; air is directed through theparticles in the carbon dioxide capture chamber, so that carbon dioxideis absorbed or captured by the sorbent. After the carbon dioxide captureis completed, the particles are directed to a carbon dioxidestripping/regeneration chamber 1106, where process heat is used toseparate carbon dioxide from the sorbent, and regenerate the sorbentcarried by the particles. The particles with the regenerated sorbent arethen directed back to a particle feed source, so that the particles withthe regenerated sorbent can be reused to adsorb or capture carbondioxide from the air.

Still further, the principles of the present invention can be followedin a method of capturing CO₂, wherein a small amount (by volume) ofeffluent gas is added to the flow of CO₂ laden air. The concentration ofCO₂ in the air is significantly increased, in comparison to the CO₂concentration in the flow of unmixed CO₂ laden air, and the fluid flowis passed through a sorbent structure that captures the CO₂ in the air.

With the foregoing disclosure in mind, it is believed that various otherways of removing carbon dioxide from a fluid, in accordance with theprinciples of this application, will become apparent to those skilled inthe art, including the use of many conventional steps and componentsthat are or shall become well-known and would be useful in carrying outthe present invention without themselves being a part of the invention.The scope of this invention is in accordance with the scope of theinvention as claimed in the following claims.

The following invention is claimed:
 1. A system for the adsorption ofcarbon dioxide from air, the system comprising a carbon dioxide capturestructure exposed to a moving flow of ambient air; the carbon dioxidecapture structure comprising a porous silica substrate having an aluminacoating on the surfaces of said substrate and on the surface of thealumina coating is supported an amine sorbent, which is capable ofbinding carbon dioxide from the moving flow of ambient air; the poroussilica substrate being a monolith having a plurality of channels passingbetween opposing surfaces of the monolith to allow the passage of airentering one end of the channel to exit at an opposite end of a channel,the alumina coating the internal surfaces of the channels; aregeneration enclosure, capable of enclosing the carbon dioxide capturestructure; and process steam-directing apparatus in fluid flowconnection with the regeneration enclosure, for separating the carbondioxide from the sorbent and regenerating the sorbent, said processsteam being at a temperature of not greater than about 120° C., wherethe porous silica substrate is comprised of a silica or a mesocellularsilica foam.
 2. A sorbent structure comprising a substrate comprising abase structure formed of a monolithic porous silica or a mesocellularsilica foam and a porous alumina coating on the surfaces of said silicasubstrate; and an amine sorbent embedded on said alumina coating; theporous silica substrate being a monolith having a plurality of channelspassing between opposing surfaces of the monolith to allow the passageof air entering one end of the channel to exit at an opposite end of achannel, the alumina coating the internal surfaces of the channels. 3.The sorbent structure of claim 2 wherein said silica substrate is apancake-shaped monolith.
 4. The sorbent structure of claim 2 whereinsaid amine sorbent is a poly(primary amine-substituted ethylene)group-containing material.
 5. The sorbent structure of claim 4 whereinsaid poly(primary amine-substituted ethylene-group containing materialis loaded at 40 to 60 percent by volume relative to the alumina coating.6. The sorbent structure of claim 2, wherein the base structure is apancake-shaped monolith formed of cordierite and having straight macrochannels extending through the monolith.
 7. The sorbent structure ofclaim 2, wherein the substrate comprises a silica porous monolith havingstraight macro channels extending through the monolith, and having theinterior walls of the channels coated with a porous alumina coating. 8.A system for removing carbon dioxide from carbon dioxide laden air, thesystem comprising: a carbon dioxide capture structure comprising aporous solid mass having a high surface area and formed of a poroussilica substrate, with a porous alumina coating on the surfaces of saidsilica substrate, and an amine sorbent, that is capable of reversiblyadsorbing, or binding, to carbon dioxide, supported on and distributedalong the surface area of the porous alumina coating; the porous silicasubstrate being a monolith wherein the length in one dimension is notgreater than about 20 inches, and having channels passing the fulllength through the one dimension of the monolith and each of the twosurfaces at each end of the one dimension to allow the passage of airentering one end of the channel to exit at an opposite end of a channel;an air conduit, open at one end to the atmosphere and at a second end tothe capture structure, for bringing a flow of carbon dioxide-ladenambient air to and through the carbon dioxide capture structure, asealable regeneration chamber capable of containing the capturestructure; an elevator structure for supporting and for moving thecapture structure between a position exposed to the ambient air and aposition sealed within the sealable regeneration chamber; exhaust pumpmeans in fluid flow connection with the sealable regeneration chamber toexhaust any atmosphere in the sealable regeneration chamber after thecapture structure has been sealed into the sealable regenerationchamber; a source of process heat steam for providing steam at atemperature of not greater than 120° C.; a valved hot fluid conduitconnected between the source of process heat steam and the sealableregeneration chamber for directing such process heat steam at the carbondioxide-loaded sorbent on the capture structure when the capturestructure is located in the sealable regeneration chamber, to stripcarbon dioxide from the sorbent; a fluid conduit for carrying thestripped carbon dioxide away from the regeneration chamber; and acollection chamber connected with the fluid conduit for collecting andholding the stripped carbon dioxide from the fluid conduit.